Book-keeping, Invoicing and Credit Control in North London

I need someone to do monthly invoices for me (approx 40 a month), chase up unpaid ones (credit control) and do my book-keeping and VAT returns. You need to be able to come and pick up relevent receipts, paperwork etc perhaps once a month. At the moment I use Quickbooks and am happy to continue doing so but am open to suggestions, as long as I can access (and understand) the records myself. On average there are about 80 bank transactions a month, and these include credit card payments and self-billed invoices too.

My tax year starts in October so we could start then, or possibly earlier if it suits.