Oh Bugger!
Well, I popped down to their premises at 16 Enterprise Estate on Moorfield Road at Guildford this morning (21st August) and the place is well and truly closed up. No sign of the notice on the window posted on one of the other threads about them, but peering through the mirrored glass windows, it looks like the place has been cleaned out - no computers, no bikes and no parts on the walls. Not at all like it was when I went in on the 28th July and ordered my bits!
Looks to me like they've done a runner! (I hope to proved wrong, but that's how it looks to me

)
I got in touch with Wunderlich via their website and got a helpful email. They are aware of the problem and are having as much trouble contacting anyone from BMWbikebits (or "Sidestand Ltd" which is the name they are registered as at Companies House) as we are.
They were able to supply me with a residential contact address for Simon Steele, who is the director of the firm and I've written to him there, but whether he still lives there or not is another matter

. It'll be interesting to see if I get a reply, but I don't hold out much hope.
I've been on to Companies house and it seems that they aren't too happy with Sidestand Ltd, as they haven't filed the required paperwork with them (annual accounts / reports I guess). Interestingly enough, Sidestand Ltd did re-register its company address from Mr Steele's apparent residence to the 16 Enterprise Estate location within the last two weeks. I wonder if that was a tactic to try to put creditors off the scent?
The guy at Companies House advised me to write again to both addresses in a couple of weeks if I get no reply and, if I still get no joy, to write to Companies House to object to Sidestand Ltd being struck off as a registered company, as this would make it difficult to recover any monies from the company administrators if it does go into official administration.
Trading Standards through "Consumer Direct" have also advised that I write again in a couple of weeks and quote the Sale Of Goods Act 1979, requiring that I be supplied the goods or given a refund within a "reasonable period." If I don't get any joy after that then Trading Standards may take the job on.
So, for the time being I guess it's a case of watch and wait, but in future I won't be paying cash in advance for stuff - It'll be credit card all the way!