I assume we are dealing with 2013/14. The tax code will be shown on your P60.
As you had an income in excess of £100,000 in 2013/14, you are not entitled to the full personal allowance for the year of £9,440 as you will read here. You lose £1 of the allowance for every £2 of income over £100,000 so,assuming you made no pension contributions other than via a deduction from your your salary or any charitable donations through the gift aid scheme, your personal allowance for 2013/14 should have been £6,284 (£9,440 - £3,156 (£106,313 - £100,000 / 2).
On an income of £106,313 and with a personal allowance, your tax liability is £33,609.60. As you paid £28,662, you would appear to be underpaid by £4,947.60 for 2013/14.
You can claim expenses against your consulting income if you incurred any but you cannot backdate any such expense incurred after 5 April 2014 now to reduce your tax for 2013/14. Once the tax year is over, thats it. Take a look here for information on self-employed expenses.
An accountant or tax adviser might be able to give you some advice based on your circumstances to help you mitigate your tax exposure. To keep your income below £100,000, you could increase your pension contributions.
I hope this helps but let me know if you have any further questions.