Financial planning, including cash flow and forecasting, will enable you to ensure you have the funds you need to carry out your activities and achieve your objectives and that you have taken all costs into account.
Once trading, businesses will need to be aware of taxes they may be liable for paying, such as VAT and Corporation Tax.
[UPDATE 20 Nov 2012] The Business Link (and DirectGov) websites have been replaced by GOV.UK
Information for established businesses and people wanting to start a new business is still available.
You should also contact the relevant HM Revenue & Customs office.
The HMRC website has useful guides and helpline numbers on tax issues for businesses.