Take off the two inner sill covers in the footwells (I'm sure there's a how to somewhere) and clean the two earthing bolts and body connections behind (one on each side), use a scotchbright pad or similar (or a disposable emery nail file) and clean any dull looking connectors and around the inner bolt face and around where the bolt/earth leads attach to the body, apply a small amount of grease (do not ever use silicone grease for electrical connections!) to the bolt and body area and re-tighten. The grease stops air getting to the cleaned surfaces and therefore prevents (re) oxidisation.
As Steve B has said, this sounds very much like an earthing fault - the clue is in the other warning lights coming on. After doing the inside, do the one behind the passenger side headlight - this is the main engine earth (also the alternator earth).
How old is the battery? The A2's suffer from low voltage to the main control electrics as there is a voltage-drop due to the long cable runs used, so a good battery is essential. Check the battery voltage at the battery: with engine off, the voltage at the battery should be 12V or higher. Engine on, it should be 13.8V. If you can, check also the voltage on the main positive lead in the passenger footwell compartment - look for a nut holding down thick cables on the CCCU/ECU holder. If you see anything around 11V or lower (and the battery volts are OK) you have poor connectivity somewhere.
Be very careful not to short the battery/electrics - if in doubt, get someone who knows what they are doing to do it as shorted batteries can explode, and the leads above are not fuse protected.
The above costs next to nothing, only time. This is a very common A2 fault