Tesco mobiles are generally locked. However, if you go on their website, they will unlock it for free.

It can take a couple of days but if you use their online chat facility as I did, it took about half an hour.

So if you are happy with your phone, then you can look for a SIM only deal.

I have no problem with my Tesco signal in Jarrow but are changing to EE SIM only when my contract with Tesco runs out, as Tesco (O2) coverage in the Lakes and Northumberland is variable. EE is much better.