Redundancy/Second Job and Income tax

Hi

I am currently in a redunancy situation and wondering if I can get some help.

I have been told by my current employer that I have to work my current notice which ends on 15th July. However I can leave early on 15th June. I have been offered 2 full time jobs and they want me to start with them ASAP.

My current employer appreciates that I want to leave and start my new job but they are refusing to let me go early - which they have reasons for and I totally understand. They have however suggested a compromise in that I can start my new job ASAP whilst im on annual leave until 15th June - I have approx 6 weeks holiday to take!

Questions

1. If I go on annual leave with my current employer until 15th June and start my new job at the same time how will this affect my tax situation?

2. My current employer has stated that they will send the P45 in June 2019 - will this have any affect in the future even tho I started the new job before the P45 has been released?

Thanks