A few points to note

1.Overheads are far cheaper in Malaysia. Hence the spreads are smaller.

2. Also unlike the UK, there are loads of small independent money changes in KL and Singapore. Competition is fierce compared with the few large bureau de change in London despite all the tourists in London.

3. Another point to note is that there are are lot of Malaysia students studying in the UK leading to high local demand for sterling giving rise to a good Sterling / Malaysian Ringgit exchange rate so there is a good market for currency exchange in Malaysia. The demand for Malaysian Ringgit in the UK is limited. I use have seen a whole year's worth of school fees paid in physical currency notes although I am not sure if that is allowed any longer