Thanks for the replies.

I did cut the seed head off some of them but the central stalk has just carried on thickening and maturing.

When I noticed they were bolting, I seeked advice from a couple of seasoned plot holders and they told me that the central part of the leek goes thick and woody and inedible. So obviously something along the growth line has gone wrong with them as I have two patches of leeks, one on the plot itself and the spares I had, I tucked into a patch of garden at home and they have done the same.

I am thinking that just maybe I have had a duff batch of seed that weren't quite up to the job.

I am going to see if I can salvage any outer parts and make up some soup with them and 'have another go next year' <rolleyessmiley>