What happens if British passport application takes over 90 days (surrender q)?

I read that there is a 90-day period within which you must surrender your Indian passport.
But what happens if the UK passport application takes longer than 90 days and you don't get it back in time?

You should be fine. It's not enforced strictly. I submitted application for surrender of indian passport after 5 months of getting british passport. No questions asked.

Not sure where you got the 90 days timeline, but HCI london website does not mention that Indian Passport has to be surrendered within 90 days. Did you get this info from official website?

Reference:
https://www.hcilondon.gov.in/page/surre ... -passport/