What's up with my broccoli?

Last June I bought 2 lots of purple sprouting broccoli 'seedlings' - one from a garden centre the other from either Homebase or B&Q (can't remember which). They were all very healthy and since I'd read they don't like their roots disturbed, was very careful when I planted them out. I followed the instructions, made them a nice cage from very fine netting to keep the cabbge whites away and was delighted when they turned into big, healthy plants, but ....... that's all they've done - turned into big healthy plants.

One plant has had one tiny spear the 'head' of which rapidly grew to about ½" and hasn't progressed from there since November, the others are just plants with ne'er a spear to be seen. Now, the label which came with them says 'Plant March - July: Harvest Oct - Feb' - but if anything is going to happen in the next 3 weeks they don't half need to get their skates on!

What have I done wrong?

 

As Loofah says, they should start sprouting in the spring. Around March/April would be the usual time for harvesting.
Don't know why the label said harvest from Oct - Feb though, I'd say that's a bit misleading as purple sprouting broccoli has always been a spring vegetable.

 

I always found it had a fairly short cropping season, especially if we get a mild spring.

It quickly runs to large flower buds if it turns mild.