You cant control when autos switch but they will still keep growing during the flowering stage. one thing to keep in mind is that if your using a 400w light its likely to be costing you 35 quid or 55 dollars a month (delete as appropriate) so if your grow costs you 70 quid/110 dollars in electric alone you'll be needing to harvest a good ounce wet that'll leave you half ounce dry (if your lucky) to make the grow break even. Thats obviously not taking into account the price of seeds, soil, nutes.
If a half ounce of weed can be bought for 80 quid/125 dollars is it really worth the potential trouble with the police?
Its a tough call i hope things pan out for you, my grow has elements that im struggling to control that may result in 3 months work coming to nothing so i feel for your situation but i guess thats just how the cookie crumbles sometimes.