So a bit of a heads up for anyone using one of these in the future.
The issue turned out to be very very fine particles of debris/grit under one of the internal return flaps.
Resolution; undo the flap and clean, turn over. Seems to be working again now, pumped a bike tyre up to 50psi so all good.
This was on advice from the Australian wholesaler of Blue Tongue who were very helpful.
Cheers
Flynny