So I decided to take action - eventually pinned it down to what I thought was a pipe connector near the front scuttle. I removed said device with the intention of rodding it through.
After trying wire and eventually a drill I realised that it was in fact a non-return valve
This has had two effects.
1) It takes a split second longer for the water to start (as expected) however, the pump is powerful and the wipers hardly have a chance to move before the water hits the screen.
2) The washer pipes under the bonnnet now no longer remain full of water and no longer freeze solid!!!!!!
I think that item 2 more than outweighs item 1
