I only moved to France for work reasons, the cost of living is ridiculous. However, very few countries have as good banking systems as the UK with free accounts and good special offers, most make you pay for a basic current account. UK bank accounts you can leave open when you leave, but you can't open from abroad.
My advice: get a good credit card you can spend on abroad before you leave: http://www.moneysavingexpert.com/travel/cheap-travel-money
Put spending money in a current account set up to pay the credit card off in full at the end of each month. If you're moving to a country with HSBC, get their account in both countries because transfers online are free now. That will pay for direct debits etc in the new country and anything you can only pay in cash.
Then get 2 santander 1-2-3 accounts for 3% interest on your first 40 grand (they are 20 grand maximum each but you can get 2).
Put any spare in the highest interest account you can find, and after you've left inform the bank that you no longer pay UK tax so they don't have to automatically deduct it any more. Don't put any more than 85 grand in any one bank as that's how much is protected if they go bump.
As an added bonus, if you regularly spend on a credit card and pay off in full you should have a pretty good credit score if and when you move back to the UK.