Are Tesco Mobile on the O2 network?

[Joe Nonety]

I read that Tesco mobile and o2 were basically the same network.
If I buy a tesco mobile phone, will an O2 simcard work in it without having to unlock the phone?

 

[msher]

no i switched over last month from o2 on pre pay,had to unblock and all that palavar,on same o2 network though