Yes, English is very widely spoken in Singapore and a little less so in HK. I have not been to Bangkok.

However if you intend to do some duty free shopping, especially in HK, stay away from the tourist areas, the main one in HK being Nathan Rd. There you will get ripped off for sure, no matter how charming or proficient in English the salesperson may be. As an example, film there is almost twice as much what you will pay for it else where, and I was almost conned into buying a fake / 2nd watch were it not for my very observent friend who is fluent in Cantonese.

Singapore is not so bad but try to stay away from the electronics shops on Orchard Rd, especially Lucky Plaza. One shop tried to sell me a mobile phone with a non genuine battery which was of course claimed to be genuine when I raised the issue.

Have a good trip.