Just to clear up:
1. HSBC Private Bank is separate from HSBC Group but owned by HSBC Holdings.
2. You can find a branch of this in Paradeplatz next door to Movenpick among other places.
3. You need GBP2M or currency equivalent. There are exceptions, but as often or not they'll expect a bit in excess of this.
4. I recommend Swissquote if you don't need a debit card. You can get a Visa credit with Swissquote - they're almost an online-only bank, though they have a cafe-esque branch off Bahnhofstrasse which is most impressive.
5. I recommend Credit Suisse over UBS as I've found the UBS internet banking login system to be most labourious.