Everyone who has a tax code will notice that it usually has a number and letter as part of the code.
Sometimes the tax code that you will be given for a particular job or income stream may be 0T (note that this is a zero not OT).
The zero denotes that you will not be given any personal allowance for the income that has been assigned the 0T tax code.
This may be because you have used up your personal allowance elsewhere, or perhaps you have started a new job and your employer does not have enough information for your tax code as yet.
The 0T tax code means that all of your income will be taxed for that income stream. The tax rate depends on how much you earn from that work/pension as to whether you will pay basic rate tax on the earnings or if you earn enough from that job (if indeed it is employment) to pay higher rate tax.
It is possible that a 0T tax code will be corrected down the line, as it is often used as an emergency measure, so if you believe that this is not correct it may be worth contacting the inland revenue to check that they have all of the correct information for you.
Once the Inland Revenue have all the up to date information they can send through the correct tax code to your employer and you may start to pay less tax that you would do on a 0T tax code.
If the tax code is corrected within the tax year then it is likely that you will get an adjustment to your tax once your employer has the correct code and that may involve effectively refunding tax from when you were on the 0T tax code by reducing the amount payable once the code has changed.
if it is near the end of the tax year when you are given the 0T tax code and it is not corrected before the end of the tax year (assuming it is wrong) you may need to reclaim overpaid tax from the Revenue.
In any case you can contact the Inland Revenue on 0300 200 3300.