If you are serving out your notice period, then you are considered to be still employed, and not eligible for Jobseekers payment until your notice period ends. When you do make your Jobseekers application you will be asked however to provide information on what efforts you have been making over the interim period to look for work.
If you have only been in employment for 7 months, then you will not receive any statutory redundancy payment, (any payment that you receive will be ex-gratia) and therefore will not receive the RP50, which is for the statutory payment.
As you are still employed until end of April you should not receive your P45 until then. If for some reason you don't get it then, you can ask for a letter to bring with you to make your Jobseekers application.