No it's not a legal requirement to have a business bank account (according to my accountant anyway) - The tax man doesn't care where you keep your money as long as you can prove it's either business money or personal money.
Most banks get a bit twitchy when you run a business through your personal account as they can make more money from you as a business customer. So technically you can use your personal account, but when the bank wise up they may make some charges.
I opened an Abbey Business Bank account, it's totally free for life as long as you keep within their agreed limiteds - it's something like banking no more than £3000 cash per month, ATM transactions only, no coinage, free cheques as long as they are kept within a certain limit, etc.
I've found it fab and really easy to set up - I chose not to have an overdraft but the facility is there if you want it. I also got a debit card so I can pay for my goods on-line etc.
Highly recommend it for us just starting out and not banking huge amounts at the moment :wink2:
Trin
xx