Thanks for the suggestions.
I went to test it again earlier. Checked the control lever was engaing on the cable. Seemed fine.
Checked the prop. Was not fouled or loose.
Then ran the engine with the weed hatch open...(no i did not sink). And it worked in both gears each time.
Ran in in gear for half an hour and checked again. Forward and reverse. Almost annoying that it worked normally. I was moored up during this test so my new thinking is the prop getting jammed up easily when moving.
Will take it for a propd spin at the weekend.
Thanks