Originally Posted by
marconess
As long as you have the correct paperwork to enter the UK (as BA will treat your first flight as ending in London, and therefore require the correct visas) and you have a boarding pass, you'll be able to head to flight connections with your hand luggage.
Unfortunately, as well documented, BA won't interline bags on separate tickets.
PS And it is not a ‘how high is your status’ thing, nobody gets this.
PPS And unless you are extremely unlucky, I do not believe that you would have to wait for 3 hours at T5 immigration.