I read thru the posts quickly, but I am not sure have you thought about the big picture, as I didnt get that what is all of the stuff that you already have currently, you just saying that you have a computer and monitors, a budget of 400£ and you are getting the interface and you need to mice the whole set.
Do you have enough cables, stands, mics, room damping material, a carpet under your drums, headphone amplifier/mixer and such? These all cost money and you can quickly spend the 400£ easily on just cables and stands alone. For example 12 good quality Cordial XLR cables with Neutrik connectors cost ~200£ and the medium quality k&m microphonestand set for the whole band (kick, snare top+bottom, three toms, two overheads, hihat, ride, spare and two for guitars and one for vocals) costs ~275£ which already goes over your budget and you don't even yet have anything to record with.
Even if you would choose the second cheapest option for mics (never buy the cheapest because they usually are really shitty!), you would still spend over 400£ on the mics. My set consists of 5 x SM57, 3 x e604, 1 x e901 and 2 x NT5 and they cost me about 975£ and it still doesn't have any studio quality mics for vocals.
I would suggest to start so that you can record with all the inputs of you can afford within your budget, I would guess that would be about max 8-16 with something + behringer ada 8000 (I was going to suggest firepod, but does it have adat option?). Practice with them, and upgrade as you get more money.