Just for info: I've contacted both Enigma and Carrs. Both asked for photos (which The Bike Chain kindly supplied). Enigma didn't respond again but Carrs were hugely friendly and helpful and assured me that they could fix it (and the quote was £45 + VAT & carriage!) - the frame is on its way to them now (again, thanks to The Bike Chain).
Only time will tell how well the repair lasts, but I've been impressed with the service from both TBC & Carrs.