I am going to Basel via London with BA on 11-11-2017.
I have a valid UK visa valid from 28-11-2017 for 6 months. I purchased a direct ticket Hyderabad to London and London to Basel with BA.
Both arrival and departure is at Terminal 5. The layover period is 21/2 hours.
Do I require a transit visa?
You seem to indicate that you have what I assume to be a visa to visit the UK with effect from 28th November.
It's not clear from your post whether or not your journey from Heathrow to Basle is on the same ticket as the journey from Hyderabad to Heathrow.
This is a matter on which you're going to have to contact BA, because they won't let you board in Hyderabad unless they're satisfied that you have all the visas which are necessary for your journey. They'll check that at check-in, or, if you check in online they'll check it at the boarding gate.
