Seeing as you have not provided much information about the culture, work-life balance etc of the respective banks, I am basing my reply on the information that has been provided i.e. the respective salaries and the lifestyle that you will be able to enjoy in the two cities respectively.
Well as you will obviously know, in the UK taxes and cost of living are sky high, apart from income tax there is still council tax, national insurance, plus all your bills and congestion charge etc. In Singapore $180,000 p.a. will get you a very very good lifestyle as taxes are low and living costs are comparatively cheap. You will get to live it up in a nice swanky
condo in the heart of town and drive a fast car, and run tabs at the most fashionable bars, if you earn $180,000.
Thats all I can say mate!