You'll need a mountain of documentation — proof of address and proof of ID — which you probably won't have if you've just arrived (especially if you're still dossing on your mates couch).
If there's one thing we can't stress enough it is: open a bank account before you leave home.
How to open a UK bank account
Find a local branch at home
If you're living in Australia or New Zealand you may be lucky enough to have a HSBC Branch near where you live. If you're close to a local branch of HSBC Australia or HSBC New Zealand you can walk in and enquire about opening a UK bank account.
You'll need ID, proof of your current bank address, statements from your other bank and a minimum deposit amount.
Consider opening a joint bank account if you are moving to the UK with your partner — it will cut down on paperwork and you'll share the minimum deposit amount.
Travelex is a foreign currency business that can help you open a UK bank account with HSBC. You will need the same documents as if you walked into a branch (see above).
Use an agent
Some companies like 1st Contact and South African company OVC (Overseas Visitors Club) will help you get the show on the road for a small fee. This is a great way of doing it because they already have established ties with several major banks and can cut through all the rubbish.
Leave it to the last minute
If you do put off this task until you arrive in London, good luck — one bank branch may issue you an account on the spot, while another will mess you around.
Get together as much documentation as possible, including proof of ID (passport, driver's licence and/or birth certificate) and evidence of your UK address (a utility bill or lease with your name on it should be enough, but not always).
It's also worth bringing a letter from your bank at home as record of your credit history, and a letter from your agency or employer in the UK. The more documentation you have, the easier your application should be.
Credit cards and overdrafts
You may be able to get a UK credit card, but it recommended you bring your Visa or Mastercard from home to use if things get tight while you are still settling in.
You can also apply for an overdraft on your main account, although the interest rates can be high - so beware of going too far into debt. Banks charge penalty rates for exceeding your overdraft limit, so be sure not to overspend.