I hope this is a wind up!

I can only go by my own experiences. Locally we have had lots of those signs showing your speed  for several  years now. In that time we have had 6 cars. All at 30 mph on the speedo have registered at 27 mph on the signs.

Assuming that others cars are similar, if you are clocked at  31mph your speedo would be showing 34 mph. If currently you are allowed 10% your speedo would be showing 36/37mph. Personally I don't consider that acceptable. You don have to monitor it that closely to see it is over half way to 40.

Yes, that’s what I thought about Metheven's posts.👍🏻

Putting my Tin Hat on.

When it comes to speed on public roads, does anyone really obey every single speed limit for every bit of road they drive on. Come folks, be honest with yourself.  I not saying its right or wrong and if you get caught then you only have yourself to blame.

Incidentally, every non major road where I live is now a 20 mph limit and nobody appears observes it although it has slowed some drivers down a little. but even the police cars and ambulance still exceed the 20 limit when just driving through. 

I obey 20mph and 30mph limits. In many built up residential and town street 30mph areas I am often doing 20mph anyway. 

I will increase speed when overtaking on a motorway to two or three mph over the limit on occasion if a vehicle is doing perhaps 67 mph in order to speed up the passing process. There are times leaving a built up area and into open country when I have sped not realising that the limit has not changed.

It’s not really about whether or not we break the speed limit but whether there should be any legitimate leeway.

I can’t claim never to have exceeded the limit - who can? It’s very easy to let our attention wander and creep a few mph over the top but, if I do that, I know I’ve only myself to blame and I don’t expect to be let off for 'only' doing 33mph when I should have ensured I didn’t exceed 30. In that scenario I’ve broken the law and deserve whatever is thrown at me.

The 10% leeway is a myth. Different police forces implement different tolerances. Some are very low indeed. Best not get caught out. Some will fine at 1 mph over. You need money to take them to court and fight your case. So easy to make a mistake on journeys in unknown areas.

"It’s not really about whether or not we break the speed limit but whether there should be any legitimate leeway."

Is it though. As you say its a honest mistake.

I think that ridiculous though and have known it happen allegedly. If I am driving at 30 mph I wont know that I have exceeded the speed limit until speedo or satnav shows 31mph which \i suppose could mean that my actual speed could be 31.5

I totally agree ET, that is information from someone who runs those driver speed training courses you can do rather than pay a fine and get the points! They rely on folks not questioning a ticket! 

My speedos fit perfectly.