Cucumber not thriving

I started to do staggered sowings this year for beans. I used to do an early crop of dwarf in the GH which I started again this year. I sowed a late batch ( with saved seed from my early sowing) but unfortunately they are still in their pots
Sowing just a couple of toms early - late Jan/early feb then doing the main batch in March also works well for me.
My cucumber plants look reasonably healthy but I think I may have picked the last one yesterday. They slowed right down a few weeks back and on checking them out earlier I can see a couple of huge fat ones turned yellow that I missed.
That said I'm ready to start making way for my new seedlings my flower sowings are beginning to sprout.