What size pet carrier

I need to buy a new pet carrier for the rabbits, what size would say i needed for a medium sized bunny.

I bought one from home bargains for 5.99. It is around cat/small dog sized, but he had enough room to move around as we were travelling for 4 hours. If it was just to go to the vets, I suppose it could be smaller.

I have one of these: http://www.zooplus.co.uk/shop/cats/...t_bags_travel/classic_black_travel_bags/13398

I can fit Smokey (who is medium sized) and Inky (who is a bit smaller) into together, so it's quite big. It's great, much easier to get them into and out of, folds flat for storage and I think they feel a bit safer in it too.

i have a large cat sized one which i bought for £15 pounds i think... it has a removable lid and a removable grate at front and at top if i want to not split the whole thing into two.... see its something like this one
http://www.zooplus.ie/bilder/pet/carrier/supra/dark/blue/1/300/45471_Transportbox_Supra_bl_1.jpg but isnt identical and i dont have the little bowl that is attatched..