I share a private house with 3 others in Fallowfield, Manchester Student Central, it's a good place to live and we have not been robbed, but we are very careful & have an alarm. We don't have locks on our bedrooms but we respect each other's property and privacy so we don't need them. By all means, if you don't trust your housemates, fit a lock. It's your peace of mind at the end of the day. I wouldn't bother locking against thieves - as mentioned, if they can get in your house they can get in your room. My housemates are like family and I can't imagine not trusting them. And not all parts of 'gunchester' are that rough, by the way.