Thanks for all the input & suggestions folks. So just to update this.. On the back of the advice here, I rang the guys on Wednesday from a private number & they picked up straight away. I asked for an update & the guy basically said they can't find the fault & having tried various things like the ABS module, ECU, gearbox ECU and a couple of other things they couldn't replicate or find the problem and he was going to give me the car back. I said ok, I'll collect it Friday. And then I got a lift straight to the garage to pick it up there & then. When I got the the car looked like it hadn't moved in 3 weeks. Cobwebs all over it & blocked in by a load of other cars. I'd say they looked at it the first day or 2 & then just left it.
So since getting it back, it seems to be fine. Starting every time no problem for the last couple of days (I have probably just jinxed that there though!!). I had a quick look around the car to see if they had done anything obvious. It does look like they checked the battery as the carpet was out of place & the contents of the boot were all over the place. Can't tell from the engine bay whether anything was done. The only thing I have noticed is that the Auto Start-Stop now appears not to be working. I'm curious about that but I'm ok with that not functioning if the car starts when it should when I first get into it. So I guess we'll drive it for now & see what happens. If the problem recurs I'll be straight into Valdas or someone else trustworthy to get it rectified. It's not due a service for another 15k so I'll get it looked at before that in any case & I'll update here if anything else develops.
But for now I suppose, all seems well. Whatever they did (connecting or disconnecting this or that) looks like it might have resolved it. Hardly scientific but need the car on the road over the next few weeks so time will tell. Nice to be back in it though I have to say.. Such a lovely place to be, especially with the darker evenings & the interior lighting & heated seats etc.. Makes it all worthwhile!
Thanks again everyone! S