I will be visiting the UK in a couple weeks and should be landing at T3. I know that SIMs can be purchased at a number of places in the terminal (vending machines, WHSmiths, or SIM Local). Has anyone gone through recently to see if the prices of the PAYG sims are the same as what you would get in the city (i.e. same as the rates the companies have posted online)?

I will be travelling to Norway and Denmark on the same trip, I would be looking for PAYG that includes roaming and it seems like 3, EE, and O2 all have those. Any recommendations between any of those?

Thanks!