Like Joe says, I'd be careful about staying longer than you stated you would be, even if you don't stay longer than the visa allows.
I have a friend whos Turkish friend applied for a tourist visa stating he planned on staying for a few weeks. He was granted a 6 month visa and chose to stay for most of that 6 months.
When he next applied for a tourist visa, he was refused on the grounds he stayed longer the first time around than he'd stated even though he didn't technically stay longer than the visa allowed.
Ultimately though, this didn't prevent him coming back to the UK as he has since married his British girlfriend and is now in the UK on a spouse visa!
