easiest way is to stick with HSBC ; they have an internet savings account which pays something like 6% on the first £50K [ last time I looked
so open internet accounts , you can transfer money in from your current account instantly , or by standing order if you prefer
only thing to look out for is that you don't get interest in any month in which there is a withdrawal .....no problem , when you have your tax demand empty the account into your current account on the first of the month and pay up , putting the surplus elsewhere
go look at their website