Thanks.
It was only MOT'd two weeks ago and nothing flagged up. I did have a look over it while it was in the air (friendly MOT guy).
It's so intermittent that I can't reproduce it on demand to start working out the cause.
If it isn't likely to be ABS, then I have two faults as I had an ABS warning yesterday.
Just re-installing VIDA at the moment to start checking the error codes. Unfortunately, in trying to get my cheap code reader (bought for the V70) to read the codes, I reset them, so the ABS warning has cleared. Hopefully it will be stored in the CPU.....