I read on a US thread about guys with poor grip and incorrectly sized tyres having this issue. 1 guy checked and had a massive difference in the rolling radius.
To be honest ( I will say it nicely before someone else doesnt ) with the way the car market is at the moment, you can buy a lot of petrol for the money you lose on its value. I was offered 9k for my 55 plate as a trade in this week