Cauliflowers not heading up
It sounds as if your cauliflowers have grown well until now and haven’t been affected by the bad weather we have been having. They will have received lots of water which they love. If the growth was checked at any time during the early stages of growth this may have affected the plants and they will produce small deformed heads. You didn’t say if you had been feeding your plants but they do benefit from a feed of high nitrogen fertiliser to boost curd formation. I would try feeding them and give them a few weeks to see if the curds grow. Sulphate of Ammonia is a rapid source of nitrogen however if you don't have any of this feed with Growmore or any other multipurpose fertiliser.
They do grow better in a fertile soil that has preferably been enriched prior to planting however you could sprinkle Pelleted Poultry Manure on top of the soil to add some nutrients.
They do mature quickly once the curds have set so if you don’t get any joy after that I would harvest the leaves and grow something else before starting again with the caulis in the autumn.