IWant - I found it much easier to open a new account. I've opened one with Barclays, fee free basic account with Debit Card, purely for my MB.
Initially I started out with £150 of my money. which I transferred to my new Barclays account. I bet, one offer at a time, withdrawing any winnings from the bookmaker and often having to wait until it went into my new bank account before being able to continue to the next bet - incredibly slow and frustrating at first! But I was determined not to 'play' with any more of my own money.
I continued until I had doubled my money and had about £300 floating around between my new bank account, various bookmakers and exchanges. THEN I transferred £150 of that back to my own, personal use bank account so that all the money I was using from then on for MB was purely profit, about £150.
That slowed me down because I was back to placing one bet at a time for a while, but my profit has now built again and I currently have around £600 between my new bank account and bookmakers/exchanges - this means I can bet a few at a time often and i'm not so limited as I already have a couple of hundred quid in my bank account to spend from immediately.
Re: profits, I haven't actually taken any yet. I intend to do MB as a long term, regular income and for that you need a decent amount of cash banked constantly to use for MB only - you can't really make £300 profit then spend it all as you'll be constantly back to stage 1 where you have to wait for credits to bet again.
I intend on going until I hit £1k and keeping that as my constant float. Then, after that, i'll wait until i'm about £500 up again, and withdraw £500 at a time from my MB bank account to my personal account, to actually use.