I'd suggest an Excel spreadsheet
AND an accountant.
There are a number of people disgruntled with their accountant on this post but this is because nobody is likely to post about how good their accountant is. I wouldn't be put off by these posters but do seek referrals and research your accountant throroughly.
If you absolutely insist on not using an accountant then have a look at
www.moneysoft.co.uk. There's a good simple book-keeping package which could suit. (I'd still get an accountant though!)