Last time i had cops come round i'd just finsihed smoking an few joints, and had a 1/4 oz on my table. They saw it, picked it up, smelled it and put it back. If it's in your own house in the UK and it's 1/4 or under they normally wont even confiscate it, if it's anymore you'll probably get a fine at the very very most. Even if it's more than an oz you'd only get a suspened sentence, so it's pretty safe in England. But if they knock you havnt got to let them in - and they cant search. They'd have to get a search warrant and by then you could smoke it all or get rid of it.