Did you give them the acidic conditions? Use rain water etc.

I would not have left them in the greenhouse but you could have left them outside. If your soil is acidic or neutral they would be OK in the ground if a sheltered spot on the east coast of Scotland can be found as they will not tolerated frosts. As soon as they had begun to flower then I would have just fed with high potash fertilser such as sulphate of potash or tomato fertiliser. As they have recently flowered then you can cut them back by about half and perhaps re-plant them outside if as said the soil conditions will permit.

My first thought was fertilizer - the wrong kind! If it was a nitrogen based fertilizer, that would foster foliage growth at the expense of fruit. Also as mentioned above, blueberries need an acidic environment to take up the proper nutrients for fruit development.

I think your best option at this point is to repot your blueberry trees in bigger pots with all new acidic based soil (peat?).

Alternatively, if you have a nice sunny place in the garden with conifers nearby, that would be the 'sweet spot' for blueberries. Conifers will naturally acidify the soil and provide perfect conditions for blueberries.

Maybe the fruit shrivelled so quickly because their skins split? Similar to tomatoes that have uneven watering or temperatures. Definitely go with ericaceous compost & fertilisers though, big pots too

Thanks for the advice. Will cut back at some point and repot and be a little more careful of watering regime next year. They were planted in ericaceous compost with ericaceous fertiliser.