Steve, thank you for reply and information provided.
Your earnings in the tax year were above £100,000.
The Personal Allowance reduces where the income is above £100,000 - by £1 for every £2 of income above the £100,000 limit. This reduction applies irrespective of age or date of birth.
You were given a tax allowance of £5,580 in your tax coding. This would have been done not knowing that your income may exceed £100k.
As your earning were above (100,000+8,105*2) = £116,210 you would lose all personal allowance.
In light of this, your tax bill for 2012-13 is
First £34,370at 20% 6,874.00
Next 86,683 at 40% 33,473.20
Tax deducted £38,111.20
Balance due 2012-13 £2,236.00
In addition, you will make a ist instalment payment of £1,118 towards your tax bill for 2013-14.
If you are not making contributions into a pension scheme, you should consider it as you would get tax relief on your contributions at your marginal rate of tax.
I hope this is helpful and answers your question.
If you have any other questions, please ask me before you rate my service – I’ll be happy to respond.