Transferred to UK Parent Company: Should I Expect a New Appointment Letter or Continuity?

I need your help with this issue. If a company in India has been shut down, resulting in an employee being transferred to the parent company in the UK, specifically London, with a work visa and salary paid in accordance with UK regulations in pounds, is the employee entitled to receive a letter stating this change, or will the service be considered continuous? Should the employee expect a new appointment letter?

Please note that the names of the Indian-based organization and the parent company are different.

Regards,
Lakshmi

On what basis did the employee get the work visa (is it HSMP)? Without the Appointment Letter from the UK Company, it wouldn't be issued at all, I guess.

Regards,
TS