It's not really possible to get anything "professional" for £400. Even second hand stuff from 6/7 years ago costs a lot more than that.
You can cheat and use a DSLR that has a movie mode. (though even most of them cost more than your budget) Sadly these don't have proper support for pro mics that require a half decent preamp or phantom power. (you can get around the phantom problem with battery powered mics like a sennheiser ME-66 with K6 power pack) Although you potentially still have issues with balanced connections (XLR) and impedance mismatches. Personally, I have a sony Z1e with a few different mics, but even this isn't movie standard as it's intended purpose is news gathering. (ENG) It can only shoot in SD (720x576i50) or HDV, which is 1440x1080i50 anamorphic 35mbit and better than that, only onto DV tape. Even that which is around 8 years old is still worth £1000 or so just for the camera. Add in the mics at ~£3-400 each and you can see why it's a damn expensive game to enter.