That sounds exactly the same as I had. Started off intermittant. Now on all the time. Investigations to continue today.Interested to see how this gets resolved. I had an intermittent ABS error on the dash at the weekend. Stopped the van, switched off and restarted a minute or two later - still there. Carried on for a bit then stopped again at some roadworks, switched off whilst I was waiting and pumped the brake pedal a couple of times just to check the pedal feel. When I switched back on, ABS light gone.
I need to do a full scan but I'm assuming it's going to be a sensor issue.