Back to report !
I checked the filters on the valve block.. all ok.
So, with heart in mouth we set off for a trip to the UK. I expected that the EAS would settle down after 20 minutes or so, and all would be well.
Not so.
It insisted on going high constantly, and I was forced to stop at every service area to reset it. After 6 or 7 stops, I decided just to let it be high, and we drove back to the uk with it like that.
First thing next morning I had a meeting so despatched my wife off to Mark Smith & Co in Bicester.
They diagnosed a faulty valve / valve block, but couldnt figure out which and so replaced the entire assy with a second hand one they had in stock for £75.
They also did a few other non related things, and at a great price. I can't recommend them highly enough. I used them previously when I had a Disco, and they were good then as well.
EAS has been perfect since. Goes up and down really quickly
Thanks all here for helpful suggestions.