where can we buy urgently fiddler crabs in UK ?

I found a terrific web page that will help you.

Dave C presents Shrimp, Crabs & Crayfish UK
http://www.shrimpcrabsandcrayfish.co.uk/Shrimp.htm?crayfishamerica.html~mainFrame
He has all the information that I think there is on the topic.

His Link page
http://www.shrimpcrabsandcrayfish.co.uk/Shrimp.htm?crayfishamerica.html~mainFrameHe
has links to all the aquatic stores you might want.

Maidenhead Aquatics
http://www.fishkeeper.co.uk/
They have aquatic shops all over southern England.

According to Dave, fiddler crabs can be a bit scarce to buy, as there
are only a few species available.  In the UK the most common is the
Red-claw crabs (Sesarma Bidens).  Although, there are a few others
that turn up occasionally (the green crab).

I hope you find your crabs.
pba