Speedo and rev counter at maximum without engine running (also odometer fault

Hi

I've just had my battery disconnected for 30 mins whilst I cleaned some contacts under the seat for the air-bag system but when I re-connected it I now have a very strange fault (air bag light fault cured). When I turn the key on, the speedometer and rev counter dials rortate clockwise to maximum (with the engine off)

I just tried driving the car to see if that would reset things but noticed that the trip meter was advancing at a very high rate and, after about 2 miles noticed that about 25000 miles has been added to my odometer reading.

I'm suspected that the ECU has ""glitched", so disconneted the power again for about a minute and re-connected. The problem remained

Can anyone advise on this fault and also advise if, assuming the ECU is faulty, will the odometer reading as of earlier today on be stored somewhere so it can be reset to the corect value when this problem is cured, or am I now stuck with a very high (false) ododmeter reading) (which will kepp increasing a high rate until the problme is cured.

Any help appreciated - MOT due in about a month !!!!