I had a good experience here the other day. I was trawling Mayfair trying to find a place to buy mobile phone credit. The shop at the front of the unit doesn’t sell it but he sent me to the back of the shop where the actual P. O was and they hooked me up. I had a load of cash on me(for once) at the time and as I was handling it the women told me that they offer cash back so that I don’t need to carry around so much cash in future, I thought that was really sweet. It’s kind of an amazing little place though, you can get sweets, cigarettes, a passport, foreign currency and post letters all in one little shop, it’s so handy!