Ever since we first purchased our car we always fill the tank till the gun clicks and the amount of mikes available to drive was always about 580. The last time we filled up a week ago the reading in the car said 520

Why is that so? Can my readings mane off or has anyone had this issue before?

Strange issue

How long have you had the car? Has the battery been disconnected? Have you/anyone who has been driving reset anything or altered any driving habits or routes?

Had the car since June and as far as I know the car hasn't has its bettary disconnected

Hmm strange do you check it every time you fill? It may just be that it has adjusted to your driving style etc over the last few tanks and also MPG does usually get a little worse during the winter months?

Check it every time to make sure we get around the same :(

You may also find you don't actually get that out of the tank anyway as it will constantly adjust as you are driving - it's usually just an estimate.

 

Best bet is to also reset the actual trip computer/mile counter so that you can compare your actual results to the estimate. 

We think it's because my other half has just been driving the car around town instead of long journeys to Aberdeen etc now and again

Could that be the reason you think?

Definitely, if you take it for a few longer journeys you may well see it improve  :)