I have always found with autumn planted onions, that the red ones are way more likely to bolt and go to seed the following spring than the brown ones. I have not tried the white ones.
You can harvest them as giant spring onions (or some call them green onions) before they bulk up. Those are expensive to buy and for £2.55 a kilo, it is worth a go. You could easily keep yourself supplied for weeks. Just pull some early and leave the rest to grow on. Keep an eye for any signs of flower stalks forming and eat those first.
If you have allium leaf miner on your allotment site, you will need to grow all of them under insect mesh, as they attack over wintering crops. If you have part of the crop ear marked for early use you can cram them in a bit