Hello!
Is it sensible that the same entry level job is paid 37k in London and 20k in Belfast?
Does the diffference in the cost of living justify that?
In London, I spend 1k per month. In Belfast, I will pay 540 per month?
Housing in Belfast is massively cheaper than in London and I think accommodation is likely to be your biggest expense.
I haven't tried living in London or Belfast recently, but Belfast is a nice city. Holiday in NI/Eire last year.
Just for laughs I had a look at property.
A 1 bedroom apartment in Belfast can be had for around £150,000.
See
http://www.rightmove.co.uk/property-for-sale/property-63714085.html for a 3 bedroom semi for under £150,000.
You won't be able to find anything anywhere near that price in London. Can't vouch for the area, but you get the picture.
The main thing to be aware of is the weather. It is a lot farther North and will be much colder and wetter than London. If you are good with that then there is some glorious countryside North of Belfast, including lots of GoT locations.
My initial thoughts are that you could live better on £20k in Belfast than on £37k in London.