Could I put a UK O2 Sim card in my IPhone?

My iphone is originally irish but my sim card network has been locked because of problems with my bill. I'm visiting London for a few days this week and I was wondering if I could put a UK Sim card into my iphone and would it work while I was away? Also my phone is unlocked

Added (1). I should also say that everything else except network works on my phone like apps with Wi-Fi etc.

If your phone is unlocked should not be a problem.

Seems like your phone is blacklisted for the billing issue. Even if it's unlocked, it can't be used with O2 SIM. You need to remove the block first and then you can use the phone with any UK SIM. You can mail this person (arghyle@rocketmail.com) who can help you get the phone unblocked.