Brussels sprouts ready for harvest?!

[catgirl]

Has anyone got the same problem (is it a problem?) as me, in that some of my Brussels sprouts plants (Bedford variety) are ready for harvesting now? I sowed them in February as recommended on the packet and planted them out around May, and I wasn't really expecting to get anything off them until the end of September at least.

I guess what I'm worrying about is that I'll eat all my sprouts now and there will be nothing left come Christmas time! How long do the plants keep on growing for?