Good call, connected up an old pump to a drill, quick drain using just the drain bolt. Then attached to a drill and it pumped away nicely. Tried the same thing with the 28 pump and nothing.

So pretty much confirmed its the pump that's knackered or blocked up somewhere. Is it worth trying an ultra sonic clean or just source another one? The oil pump is the last thing I want to fail or be worrying about!

Thanks for your help and suggestions.

Leigh