What's going on with my broccoli

I've got 8 broccoli plants in well drained raised beds, they're growing well with decent foliage and one or two have dense looking heads but most of the heads are really large but loose and thin.

Any ideas what I need to do? Never grown broccoli before so not sure what to expect.

 

When they go loose it means you have left them too long.
They are showing yellow flowers.

What kind of Broccoli is it?

 

2 reasons, 1 the soil is too loose they are planted in, it needs to be really firm. 2 because of the weather they are under watered, hence the "blowing" of the heads.

 

@daitheplant .

Am I old fashioned?

It looks to me like purple sprouting, which I always sowed in early June the overwintered for forming heads in the following spring.
Now I see seedlings of this available in April for planting out?

To me, summer broccoli was always calabrese which was a summer greens and not for overwintering.

 

You are colour blind Pete, there is no way that is purple.

 

ok so its not purple, but pic one does not look like calabrese to me.

 

But then again in pic two it does appear to have courgette and potato encroaching on it.