Hi Athlete95,
I am sure I read somewhere that if you take public transport and are delayed, as long as your flights are on one pnr Ba will help you out. If you are in a private car/taxi I am not so sure.

Anyway I often use taxis and even on the worst day it took under 2 hours the m25 was shut but the taxi driver did know the back roads.
I would be more concerned that the jersey flight is late, as you know it often is. If you land after the 3 hour minimum BA will defiantly put you up and rebook if needed, i made a connection with just under 2 hours on the clock as we left lgw on the way to lhr.

But you should make it, what day are you travelling......don't say Friday! Worst day of he week on the M25 at that time.