Thinking of Starting a Grow in Uk

Okay, so im thinking of starting a grow. the cupboard i have chosen is in my girlfriends semi and i have a 3 month old son who sleeps in the room where i have chosen to grow it in, i didnt want to but have no choice if i am going to do it. the cupboard will have a lock on the door so i will be the only one with access. i am only planning on having four plants growing in there max, with a 250cfl and a 400w hps for flowering, carbon filter and exhaust fan+ soils etc. it is for personal use so there will be no suspicion of selling. i am not telling any one about this grow apart from my gf, she wont tell anyone.
Question1. if i say that i was the only one who knew about the grow and she denies any knowledge of it will this make a more serious case gainst me as her name is the name on the lease or the house ?
2. what is the punishment for this amount of growing?
3. could i claim the plants are my own although she new, but me take full responsibility ?
4. the exhaust is getting pumped into a loft, would these bulbs give off enough heat for a helicopter to pick up on thermal imaging ?
5. what do yous all think my chances of getting caught are ?

thanks for the help people am i too paranoid ????
4.

You're too paranoid.

but i'll answer so far as i'm aware which might be totlaly off haha

1. The court will dismiss this defence, they'll say no way women being women she wopuldn't have looked or worked it out or found you tending them etc etc
2. there is plenty of precedent set in the UK, it varies from court to court but for 4 plants, a slap on the wrist and a fine, depending on your situation, maybe a few hours community service
3. don't think they'll buy it, and don't think they'd think it serious enough to offer a plea bargain
4. yes, but so do 1001 other perfectly legal household appliances, they might take a guess and knock on your door trying to get you to invite them in, but they will not receive a search warrant for a heat signature unless in a very extreme case.
5. Keep ya mouth shut, don't try and showoff, be especially careful when drinking, don't make it too obvious to friends how much weed you have or of how much you know about the weed in question, and you'll be just dandy.