What's up with my Cucumbers?

I have 4 cucumber plants in my greenhouse this year and a few weeks ago the largest ones fruit, (which had healthy fruit at the bottom of the plant), suddenly started turning yellow and then brown. Now it has happened to the other 3, all of which also have healthy fruit at the base.

The first one has now after a month (ish) started growing what looks like healthy fruit again near the top of the plant.

Does anyone know what has caused this? There is no sign of pests or deficiency in the leaves? I did notice this happen to some of my plants in previous years but just thought it was something I was doing wrong (which it still could be)! They also started to grow healthy fruit after loosing some.

The pic shows one of the plants with a healthy fruit and one shriveled one above it.

 

Once the plants forms a few good fruit it aborts any new ones, until you start cutting the fully formed ones.
The answer is to keep cutting once they reach a decent size.

 

Ah, that would explain why the first plant has now got new healthy looking fruit on it after I took all the others off a few weeks ago.

Off out to the greenhouse now to cut all the rest off

ETA - now done, here's hoping for lots more fruit soon