Hi Greenie, I would say that the cable has possibly 'kinked' as this happened to mine, ensure that it hasn't, if it isn't mate I'm unsure to be honest.
Re the legal stuff, you are right it is illegal to not know what speed you are doing in this country, also it looks like you are falsifying your mileage - which I dare say they wouldn't take too kindly to either...... however you would have to be monumentally unlucky to be caught for it tho!!
I have also sent you a message re that MK1 bumper which you/your mate had for sale, you still got it?
Mix