personally i use fluros right through vegging. You should be able to use your 400w light although heat may be an issue in a closet unless you got good ventilation. If you use your 400w light use mh for veg then switch to hps for flowering.
MH but cfl's will do a great job to just try get 6500k spec but hps will do just as long as you dont put it to near them cause they'll get heat stressed very easy when there seedlings!
Good point I use cfls to flower. Got 2 x 250w plug and grow cfls, you can get these in the uk at a decent price and i am sure you get them in the right spectrum for vegging too