You can also get cheap dental and haircuts in Mexico: what's Singapore's purchasing power parity compared to the UK? Maybe not an extreme difference since Singapore has has such a high GDP or even worse, but if it is more that can explain a lot even for advanced services.
Purchasing power parity depends a lot on what basket you compare.
Eg owning a car or cigarettes are very expensive here. But eating out starts much cheaper than in the UK. (There's no upper limit in either place, of course.)
