I wish you success david, there are some importantthings to consider:
You will need to have money to pay your bills while you are building up work, it is vitally important that you have this finance in place NOW so that you don't hit a crisis point in a few months time.
Economise where necessary, but if you don't have savings to pay at least 6 months equivalent of your previous salary, you will need to organize a loan.
You will find that as soon as your bank sees that a regular salary has stopped going into your account they will most likely cancel or decrease any overdraft you have arranged, regardless of your credit history.
You will also find it extremely difficult to obtain a business loan, as you will have no accounts to show (being a new business). Almost certainly you will need to obtain an unsecured personal loan. Shop around for the best rates, and remember that when your accounts are prepared at the end of the tax year, you will be able to claim some tax relief on the interest of this loan. (this is known as interest on capital)
You must also inform the Inland Revenue that you have commenced self-employed work (you have 3 months to do this or face a £100 penalty), and start to pay NI contributions every quarter (approx £30 per qtr).
Also, you are now responsible for your own retirement arrangements, so it is wise to take professional advice with regard to a stakeholder pension.
And remember, being your own boss is fun.
-Philip