Enter the UK with a valid old visa and leave the country with a new one

[M-N]

Dear all

I am very sorry if this question doesn’t fit well with the category. My mother is visiting my family with a tourist visa. Her old visa will expire on 14 January 2024 and she has already applied for and been granted a new visa which will be valid from 15 January. UKVI doesn’t cancel her old visa when granting her a new one.

So can she start her visit when her old visa is still valid (before 14 Jan) and leave the country after the new visa becomes valid (after 15 Jan)? If she does that, will it affect the validity of her new 10 year visa and will she be refused entry next time? Thank you very much.

[Ticktack]

general-uk-immigration-forum/multiple-u ... 42062.html

I answered this similar question in the link above.

[M-N]

Thank you very much for your response.