Re: $ to pound £
It's in Manchester.
I think the industry sector is also relevant. You see a lot of very well paid jobs in London, the best paid are in banking/finance, and many of them require finance experience as well as tech skills (also degrees but that's a different article).
I'd say it's inevitable that if you say you live in London, and you don't work in finance, the salary calculator will suggest you're massively underpaid. At least it did for me......