Occasional starting issue - transit 64 plate, H2L3

[escapewheel]

I wondered if anyone could help?
I have the transit 3.5 '64 plate... every now and then when i turn the key start it, the engine is very lumpy/ choppy and when it does start (if i am lucky), the engine is initially barely running. Its very odd because the next time i go along to start it, its fine!
I had a new battery 2 years ago, a new alternator 8 months ago and had a new starter motor several years ago. Can anyone try to expalin what is going on here?
The van had the same issue 12 months ago but that day it didn't start and had to be recovered by RAC as on that occasion it was the old battery.
Surely it can't be the battery again as this one was new about 2 years ago (or less) and is a good quality one.
Hope I have descibed the problem i am having, clear enough.
Thank you for any replies. i seem to be haunted by this ongoing problem. The transit that i had before - old shape '05 plate was never any trouble at all, and the best van I ever had!
Best regards