Mine were very weedy last year and they only really made it to 'baby leek' size. But you say yours haven't even made it to pencil thickness by late Oct? That is rather small. I think mine were like pencils in late summer, and by winter, they'd got as big as... sausages (? is that a recognized measure of leeks? ;D ) After that, they never grew any more.
However as the others say, if they survive, they'll still taste nice, so maybe leave them? Are you really short of space, even in winter? Or could you do onions as well in a different patch?