I live in the UK. I have a non resident friend who wants to invest his money and set up a business here. He asked me to do an enquiry about opening a private bank account. This will be his first step for submitting a business visa application to migrate here. Any idea if it is possible for a non resident to open a bank account in the UK? What do I need and where do I start? Thank you.
This was pretty much said in a comment, but I think it deserves to be an answer.
Have your friend get in touch with a bank and communicate with them directly.
Absolutely do not open an account for your friend. At best, doing so is likely legally dubious and won't help your friend; at worst, that's scammer (or money launderer) territory as well as outright illegal.
Banks do differ in their willingness to cater to international clients, so your friend might have to do a little shopping around especially if they want to find a bank that makes the process easy. The easiest is probably if there is a bank with a business presence both in the UK and in your friend's current country of residence, as the bank will, at a minimum, need to meet the "know your customer" regulations, and that's easier if you're able to walk into a bank office and talk to someone in person (and even if not, being in the same jurisdiction helps with paperwork). The big-name banks are probably a safer bet than small ones for catering to international clients, but I wouldn't categorically rule out the smaller banks either. As said, it'll take a bit of shopping around.
Once your friend is a legal resident of the UK with an established presence, things should become much easier.