The document is the National Police Chiefs' Council, Guidance on the Enforcement and Disposal of Speeding Offences (2025), version 2.0. It is public, it supersedes all earlier national guidance, and it is a great deal more useful than the folklore version.
It is also more honest than most of what is written about it, including by people selling appeals.
There is no tolerance. There is a threshold. They are not the same thing.
Start with the law, because the guidance is not it. Section 89(1) of the Road Traffic Regulation Act 1984provides that a person who drives "at a speed exceeding a limit imposed by or under any enactment" is guilty of an offence. There is no second sentence adding a margin. Twenty-one in a 20 is the offence, complete.
What the guidance does is tell forces when to acton an offence that has already been committed. Paragraph 5.1 puts it plainly: the thresholds exist "so that police forces can be consistent in their approach when dealing with those committing speeding offences". Note the wording. Not deciding whether an offence occurred. Dealing with people who have already committed one.
Then, at paragraph 5.2, the NPCC says the quiet part out loud:
That is the police describing the national misconception, in a document they published on purpose.
The two numbers everyone runs together
There is a device tolerance and there is an enforcement threshold. Different numbers, different reasons, and confusing them is where most of the bad advice online comes from.
The device tolerance is the limit plus 2 mph, or plus 3% above 66 mph. It is not leniency. Paragraph 5.4 explains that type approved devices "are required to give a positive error no larger than 2 mph or 3% above 66 mph, it is therefore possible to enforce against these tolerances". It is the equipment's permitted error, and the last clause says enforcement at that level is possible.
The enforcement threshold is the limit plus 10% plus 2. That is the number people mean, and it is the speed at which a force would normally take formal action.
The table, and the column heading that catches people out
This is section 5.6 of the guidance.
| Speed limit | Device tolerance | Course, from | Course, to | Fixed penalty, from | Summons in all other cases and from |
|---|---|---|---|---|---|
| 20 mph | 22 | 24 | 31 | 24 | 35 |
| 30 mph | 32 | 35 | 42 | 35 | 50 |
| 40 mph | 42 | 46 | 53 | 46 | 66 |
| 50 mph | 52 | 57 | 64 | 57 | 76 |
| 60 mph | 62 | 68 | 75 | 68 | 86 |
| 70 mph | 73 | 79 | 86 | 79 | 96 |
Four things the guidance says that kill four popular arguments
"I was under the threshold, so they cannot prosecute." Paragraph 5.3: "Nothing in this guidance restricts police forces from prosecuting for speeds falling below the thresholds." It adds that such decisions should be taken case by case with due regard to the circumstances and to the signage and engineering in place, which is worth knowing. But the first sentence is the answer.
"I am entitled to a course." Paragraph 4.8: "An offender has no automatic right to NSAC irrespective of how low the offending speed was." Paragraph 4.7 calls a course a diversion from prosecution "offered at the discretion of the enforcing police force". Paragraph 4.9 rules you out entirely if you have done one in the previous three years.
"They have to follow their own guidance." Paragraphs 1.1 and 1.2 say every Chief Constable is "free to set local policy and process against local priorities and community concerns" and that nothing in the guidance prevents that. Your force may lawfully differ from the table.
"This is a legal argument." Paragraph 1.5: "This NPCC guidance document does not amount to legal advice." A magistrate cannot acquit you because a force departed from NPCC policy.
The one thing in here that is genuinely worth using
If your recorded speed sits in the course or fixed penalty band and you were prosecuted anyway, it is reasonable to ask the prosecutor why, and whether a course was considered.
The guidance opens that door itself. Paragraph 3.6 accepts that most speeding offences are camera detected and that "due to their very nature, they do not account for any mitigating factors. This can create a perceived lack of procedural justice and fairness." Paragraph 3.7 says discretion and professional judgement matter "when it can be applied".
You are asking a human being to look at something a machine decided. It is a modest ask, it is sometimes granted, and it is not a defence.
What you should actually be checking
While everyone argues about tolerances, the point that can end a speeding prosecution outright gets ignored.
Section 1 of the Road Traffic Offenders Act 1988says a person "shall not be convicted" of certain offences unless, within fourteen days of the offence, a notice of intended prosecution was served on them or on the registered keeper. Schedule 1 paragraph 1A(c) confirms this reaches a section 89(1) speeding charge.
Fourteen days, from the offence, not from when you found out. There are exceptions in section 2, including where an accident occurred, where a fixed penalty notice was given, and where the court is satisfied your details could not with reasonable diligence have been ascertained in time. But it is a bar on conviction, not a technicality to be waved through.
Two other things worth knowing. The information must be laid within six months of the offence under section 127 of the Magistrates' Courts Act 1980, and the longer evidence based limit in section 6 of the 1988 Act does not apply to speeding, because Schedule 1 paragraph 2 does not list it. And under section 20(8) of that Act, a defendant who serves notice at least three days before a hearing can require the person who signed the camera certificate to attend.
The honest summary
Most people charged with speeding are guilty and will be convicted. The tolerance is not a right. The course is not a right. The guidance is not law. Anyone telling you otherwise is selling you something.
What is worth doing is narrow and specific. Check whether the notice of intended prosecution was served in time. Check whether your speed fell in the course band and whether a course was offered. And if you are going to plead guilty, do it before the deadline, because the reduction for an early plea is the one saving reliably available to you.
Sources: NPCC, Guidance on the Enforcement and Disposal of Speeding Offences (2025), version 2.0, paragraphs 1.1, 1.2, 1.5, 3.4, 3.6, 3.7, 4.7, 4.8, 4.9 and 5.1 to 5.6. Road Traffic Regulation Act 1984 s.89(1). Road Traffic Offenders Act 1988 ss.1, 2, 20 and Schedule 1. Magistrates' Courts Act 1980 s.127. This article is information, not legal advice. A speeding charge is a criminal matter and you are entitled to take advice on it.
Frequently asked questions
Is there a legal tolerance on speed limits?
No. Section 89(1) of the Road Traffic Regulation Act 1984 makes it an offence to drive at a speed exceeding a limit imposed by or under any enactment. Twenty-one miles per hour in a 20 is the offence complete. The 10% plus 2 figure is enforcement policy addressed to police forces, and the NPCC guidance says at paragraph 1.5 that it does not amount to legal advice. No magistrate can acquit on it.
What is the difference between the device tolerance and the enforcement threshold?
They are two different numbers and people run them together constantly. The device tolerance is the limit plus 2 mph, or plus 3% above 66 mph, and it exists because type approved speed measuring equipment is permitted a positive error of that size. The enforcement threshold is the limit plus 10% plus 2, and it is the speed at which a force would normally take formal action. For a 20 mph limit those numbers are 22 and 24.
If I was under the threshold, will my ticket be cancelled?
Not as of right. Paragraph 5.3 of the NPCC guidance says nothing in it restricts police forces from prosecuting for speeds falling below the thresholds. It does add that such decisions should be taken case by case with regard to the circumstances and to the signage and engineering in place at the time. So it is a request to the prosecutor to exercise discretion, not a ground of challenge.
Am I entitled to a speed awareness course instead?
No. Paragraph 4.8 is blunt: an offender has no automatic right to a National Speed Awareness Course irrespective of how low the offending speed was. Paragraph 4.7 describes a course as a diversion from prosecution offered at the discretion of the enforcing police force. And paragraph 4.9 makes you ineligible if you have attended one in the previous three years.
Do all police forces use the same numbers?
No, and the guidance does not require them to. Paragraphs 1.1 and 1.2 preserve each Chief Constable’s freedom to set local policy and process against local priorities. Dyfed-Powys Police, for example, publicly apply 10% plus 4 in 20 mph limits following the change to the default limit in Wales. Check the policy of the force that issued your notice.
I was summonsed to court at a low speed. Is that outside the guidance?
Probably not, and this is the most common misreading of the table. The final column is headed Summons in all other cases and from, so a summons is the residual disposal as well as the high speed one. Paragraph 3.4 also gives examples where a summons at relatively low speed is appropriate, such as near a school at certain times of day, where there were vulnerable road users nearby, or in adverse weather.
So is any of this worth raising at all?
One thing is. If your speed falls in the course or fixed penalty band and you were prosecuted instead, it is reasonable to ask the prosecutor why, and whether a course was considered. Paragraph 3.6 accepts that camera detections do not account for any mitigating factors and that this can create a perceived lack of procedural justice and fairness. You are asking a person to look at what a machine decided. That is not a defence and it will not be treated as one.
What should I actually be checking on a speeding notice?
The Notice of Intended Prosecution. Section 1 of the Road Traffic Offenders Act 1988 provides that a person shall not be convicted unless, within fourteen days of the offence, a notice was served on them or on the registered keeper. Schedule 1 paragraph 1A(c) confirms this applies to a section 89(1) speeding charge. There are exceptions in section 2, but the requirement is a bar on conviction rather than a technicality.
How long do the police have to bring a speeding charge?
Six months from the date of the offence, under section 127 of the Magistrates’ Courts Act 1980. The longer evidence based limit in section 6 of the Road Traffic Offenders Act 1988 does not apply, because Schedule 1 paragraph 2 to that Act lists the offences section 6 reaches and speeding is not among them. There is no three year long stop for a speeding charge.
Check the notice before you argue the speed.
The tolerance is the argument everyone runs and nobody wins. The fourteen day notice requirement is the one that can end a prosecution, and almost nobody checks it.
We do not sell anything for a speeding charge. Everything we have on it is free, and it is listed below.
More on speeding, all free
We do not sell anything for a speeding charge. It is a criminal matter and every letter we sell concerns a civil penalty.
What to do in the first fourteen days
The four deadlines that run from the day of the offence, and the checklist.
Is your camera fine criminal or civil?
Start here if you are not sure what you have. A civil penalty is a different thing entirely.
The 14 day notice rule, and deemed service
The point that can end a prosecution, and the rule that defeats most people who try it.
Section 172: naming the driver
A separate offence carrying 6 points, against 3 for the speeding itself.