Your total approx earnings are therefore �40,000, after taking into consideration your personal allowances �5225 (for 2007/08) you have taxable income of �34,775 for the year.
As you will see from the attached link the higher rates threshold for this current tax year is �34,600 - so yes you will pay a little bit of tax at 40% but this can be reduced if you have any covenanted payments to charity , pension payments, or expenses you have incurred personally which are wholly in connection with your employment, for example.
http://www.hmrc.gov.uk/rates/it.htm