Yes Alan that struck me as not quite right so I've just been down the shed (damn it's cold in there), I already had the rocker covers of so took out plugs and slowly turned it over, Duncan there is no point where both inlet valves are on the move together, one should get right home before you can see the other move, looks like maybe the sticky valve is a good possibility .
I had a similar thing with my exhaust valves one was a bit sticky, it would just stay down for a little while and then flick up, possible this is happening to your inlet.
Also tried out the Chow Mien compression tester, ummm first off the Krypton factor bit, amazing number of bits to screw/plug together ( is this correct ) then I got nothing, I probable have not got it all screwed up tight enough and the cold was getting to me, I'll try it again later when the heaters on.