Hi I had noticed my car was doing low mpg but actually its not counting miles correctly (it clocked 2 miles to work today which is actually closer to 5 miles). Any idea what sensor has gone down? I have an ABS light on at the moment which hasn't cleared since I have a brake cylinder leak could it be associated. Many thanks.

Sort out the ABS sensor and the speedo will work correctly.

As the milometer is based on the speed, won't the speedo be out too?! Therefore with those ratios when you are doing 50mph the speedo would be reading 20mph?!