But it's not a legal defence. Your speedo is allowed to be 10% inaccurate and it always reads 10% over, pretty much (except my MG which reads 25% under but that's another story)
therefore, to be sure you are doing less than 30, you should drive with the speedo on 27. That's the legal counter-argument.
having said that, police guidlines are 10% plus 3 mph. so 36 in a 30, 47 in a 40, 80 in a 70. But that doesn't mean they can't do you for doing less than that.
(, Wed 13 May 2009, 9:53, archived)
(, Wed 13 May 2009, 9:56, archived)
(, Wed 13 May 2009, 9:58, archived)
if you mean slower, because out of THAT LONDON (yes there are places you know) most 30s are small villages and are a complete waste of time. 20 years ago I was caught doing 49 in a 30 on the edge of a little village in Staffordshire. Nowadays you might get banned for that, regardless of context. Then I was let off because, and I quote Her Majesty's Constabulary "It's the most stupid 30 zone in the county, but we have to police it because the rich locals complain unless it's them speeding. Have a nice day"
Context is the problem. We broadly apply speed limits and then enforce them for revenue, not safety reasons. It's stupid, pathetic and counter-productive in safety stakes.
(, Wed 13 May 2009, 10:01, archived)