You forget there's tax. Once you count tax in it's not far from B4.

You'll only earn around 66000 pounds after tax. If your rent is 1000 pounds (standard for central London) you earn 54000 pounds. That's about SGD 98,000. If your rent is 2000 pounds, you'll only earn 42,000 pounds a year which is SGD 76,000. Cost of flights twice a year removes a further SGD 4000.

Your living expenses will also be a lot higher.