What to do with your P45
The P45 is a four part form generated by the employer when an individual leaves a paid job. When you leave the Armed Forces one will be generated for you and sent to your address as it appears on JPA.
The P45 contains your name and National Insurance Number and information about your pay, your tax code and the tax you have paid up to your point of discharge.
The information on the P45 will enable your new employer to tax you. In the absence of a P45, you will normally be taxed at a straight 20% with no personal allowance. Once you hand over the form, your tax position will be corrected in subsequent months.
If you have no job to go to but are looking for one, it is worth signing on at Job Centre Plus. When you then get a job, Job Centre Plus will update the P45 and give it back to you to pass to your new employer.
If you are not going to work, send it back to HMRC. If you are going to be self-employed, send it back to HMRC or shred it.