That s an easy one, take your business (current account) elsewhere and open up a business account with the new bank.If you don t like the decision the bank has made then you can take it to the banking ombundsman but ultimately it is the banks decision (a case of their house, their rules).The only reason the banks insist on separate accounts is so they can charge you more.The believe that business accounts generate more work for them (amount of transactions) and therefore bang you with more charges.If you read the terms and conditions of your current account there is probably something in there which says you can t use it as a business account.Just take your business elsewhere.
If they told you that you had to have a business account and you didn t you could take action. The fact that you have now had a bank account declined actually means they will have affected your credit rating.I suggest you do some solid research into what you do and don t need to do so that you are prepared with the facts.