P45 Part 1A

I left my old employment ant the end of February, after which I was provided P45 form. I am starting a new employment this month (March) and I sent them Part 2 and 3 of P45 as instructed by the document, but my new employer is now asking me to send Part 1A as well. They motivate this with the fact that they need to know how much I earned in my previous employment in order to prepare a P60 later for the whole tax year. Can you confirm I can share the Part 1A with my new employer? The Part 1A even says the employer should return this part to the employee if they have received this.

Hi PA28-161,
No the part 1A is for your record and not for the new employer.
If previous pay and tax details need to be sent to your new employer HMRC will issue a code with these details. 
Thank you. 

Thank you HMRC Admin 25. The code with pay and tax details issued by HMRC, is that requested by the new employer or the employee? Appreciate if you could provide instructions on how to request this code.

Hi PA28-161,
If you change job once the starter details are received from your new employer by HMRC, if an amend code is needed with previous pay and tax this will be issued by HMRC. 
Thank you.