Hi Deedee,
First of all: have you ever registered with Inland Revenue and get a National Insurance Number?

You have 2 options:
1- You have registered to get a NIN during the period
You should have a P60 form that is issued to employees by their employer at the end of each tax year, which runs from April 6 one year to April 5 the next. It shows your pay for the previous tax year and the amount of tax and National Insurance contributions that have been deducted. It will also show any contributions you've made to a company pension scheme. You'll need this form if you get a tax return to fill in.

If you've got one, you can claim some tax back for the period before where you were with a temporary number (or emergency number).
In that case you need to send the P60 that covers that period to IR with a letter. You will find an exemple of the document to send here: <http://www.easyexpat.com/london_en/work_taxes.htm>

Using the method explained on that page, you should be able to calculate your tax. By deducting what you've paid already you will find the amount that you should get back. You can also go there: <http://www.1stcontact-tax-refunds.co.uk/>

2- You have never been registered and have just got the P45 for each time you finished your work period
In that case, when you leave work you get a form P45 from your employer and you may be entitled to a tax repayment.
You must ask for a repayment claim form P50 which you should complete and return to your Tax Office with your P45 Parts 2 and 3 if you have them.
You should get a refund within a month.
You should be able to calculate you tax refund the same way as explained in 1/.

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