Thanks for the info, I purchased some marine grade 19mm ID rubber hose which fits perfectly.
After reading through the workshop manual and re-testing the bov I think it is working OK and I have refitted it. As the new hoses were straight bits its now mounted sideways as I couldnt really get it to sit in the original orientation without kinking the hoses.
I have also been going round replacing every bit of vacuume hose I can but the car is still only making about 0.5 bar on the first turbo and 0.6 on the second. It pulls well, no smoke and there is a definate exhause note change as the 2nd turbo comes on so I think the sequential system is working OK. It will also make positive boost from 2k rpm on even very light thottle so I think the turbos themselves must be at least reasonably healthy (Or am I deluding myself?)
My next port of call is to check the intercooler and its hoses. I seem to remeber reading a post where somone used a big inner tube to test the intercooler but I cant find it, can anyone remeber what it was?