Sorry about your motorbike, and sorry you have to pass UK MOT with a 17+ year old car. That's a challenge in and of itself. You guys have some serious regulations.
Something that MB Doc hasn't mentioned is the contact ring behind the steering wheel. I'm not an expert, but I do have a 190E and the ABS light flickered on and off, and sometimes stayed on as I drove it. This car sat in a garage for five years without having been driven (it's my father's out on loan to me). I know that flaky connections can be flaky for a while and then just go out after a certain point. You could try disconnecting the battery, removing the steering wheel, and cleaning the contact ring. Might be as MB Doc suggested and probably is, but checking this is cheapest. Good Luck

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)