cucumbers - slow?

My cucumbers seem to be really slow this year, despite the warmth? I have had plenty of flowers (in fact too many of the male flowers that seem to be able to appear overnight!), and even have some female flowers with the wee fruit behind them but they aren't getting on with the job of providing me with cucumbers!

By comparison, the courgettes planted at the same time have provided me with a couple of rather large fruits.

What am I doing wrong?

 

Funnily enough lolimac mine are Telegraph; the plants look happy enough in themselves, and there are wee fruits on them showing signs of swelling, but it just seems as though I am waiting an awful lot longer than I did last year for fruit.

pete - they are in the greenhouse, although with the current weather the windows etc have been open pretty much 24/7; I'm aware that they shouldn't have the male flowers pollinated as it makes the fruit bitter - does that also apply to the female flowers? If so, I could well be stuffed as I'm not even sure that I have been getting the male flowers off in time, but I know for sure that I haven't done any of the female ones.