Different location, different comparable pay scales, different tax regimes, different costs of living. Singapore now has the 10th most expensive cost of living in the world. Beats London by a mile. Also, you cannot add your and your wife's salaries to compare with yours alone in London. Lastly, you cannot argue with prevailing wages in the country & community. 60,000 is more than you make in S'pore. SGD110,000 = 46,164 pounds. But rents are about double in S'pore, to compare cost of living. And 60k is about double "good" wages in UK. Very highly paid, by UK standards.
Tough call. What happens if you do not take the transfer? Is there any promotion involved here, or benes to your future career path? Will your wife be able to work in UK? You have to compare a lot of factors, not just the money. Most important is your future prospects with your company. If you turn this down, is it the end of your career?