Temporary Tax Codes - employed

The understanding of all of the new uses for code 0T from April 2011 is as follows:

If a new employee does not provide a form P45 and does not complete form P46 before the first payday

Using HMRC’s Online Services or payroll systems that have online filing facilities, the employer must enter either A, B or C when indicating which P46 Box is checked – it cannot be left blank. Currently, where online services are used for filing, code BR is allocated automatically if Box C is checked. From April 2011, if Box C is checked, the code 0T (non-cumulative w1/m1) if no P46 has been completed before the first payday or the new employee has not ticked any box, or code BR (cumulative) if the new employee has another job or receives a state or occupational pension.
The normal temp. code should be 747L (W1/M1)for year 06/04/2011 onwards.
In a nutshell the W1 / M1 means you are paid as if you are on week 1 or month 1 so no account of tax paid so far in the current tax year is made.
Most paye systems are filed online immediately so the tax code should catch up within a few weeks.
The best advise if you do not want temporary tax codes is to settle in the job so the code settles.