Need to restore an unlocked iPhone - Will it still be unlocked?

The camera shutter on my iPhone 4 won't open, and I've read I should try to restore the iPhone before I see a genius. The phone was once on Tesco Mobile, who unlocked it for me when I left the network to move abroad- I didn't unlock it myself at home or anything.

If I restore the iPhone, will it still be unlocked? or will it be again locked to the original network?

Thanks for any help