MFD gets its speed from?

Coming home on Friday night, going round a tight corner my ABS and ASR lights come on, I continued onto my next stop, noting no difference in performance/braking etc.

After my next stop (car switched off for 90 minutes) both lights were out for the first ~20 seconds of driving then came on again.

Reading a few threads over the weekend I see that the steering angle sensor failure is common on early Fabias, mine's an 05 so shouldn't have the older sensor.

Had both front wheels off at the weekend just to see if my enthusiastic cornering had caught an ABS sensor on the tyre (not really likely but you never know), both looked OK and were seated OK.

Same issue going to work this morning, although had a bit of fun as I braked into the first turning 100 yards after leaving home, before the system worked out there was an issue, it saw me braking and one wheel going much slower and decided to cut the ABS in, interesting at such slow speed!

Anyway, more significantly, going to work (50 miles) I noticed my average MPG was really struggling to get into the mid/late 20's! When its normally high 50's. I know it's a cold morning and my Ibiza used to drop 5mpg over winter but high 20's is a joke.

No excessive smoke etc and the car still performing (very) well.

On the way home tonight I decided to check the trip average speed, only 21mph, this should be mid 40's so something's clearly not right, then trip distance, only 7 miles yet I was about double that from the office.

Then I checked the speedo miles and trip miles on the dash (not MFD) and it appears they're only going up at half reality.

So, what sensor gives the MFD its wheel speed and clearly the miles/consumption etc is all calculated from that? As mine appears to be only reading half.

I'm guessing it must be the ABS sensor given the dash lights and scenario under braking this morning, is this prone to failure? Given its reading half speed is it not a toothed CV its reading off but something else?

Glad its not a fuelling/ECU/engine issue with regards to consumption and should be a simple fix as long as its a sensor rather than a CV.

Unfortunately a guy at work has my vagcom cable but I should have that tomorrow, but any thoughts appreciated.

Thanks

Chris