purple sprouting broccoli has bolted!

Hi all,

Was excited to get the the plot this weekend as thought I would be harvesting my long awaited purple sprouting broccoli. Have been nurturing these for months. Had checked them last week and one plant was starting to develop the lovely little purple heads.

But instead I found a mass of yellow flowers! Is there any way back for my plant? Whats the best way of harvesting/ looking after my other 3 plants to stop this from happening?

Thanks,

Will have to keep a really close eye on the others!