Never Heard of Such a Policy, But...
I've personally never heard of such a rule, but I've also never flown into LHR. Even old farts like me can grasp the logic. It is not an unreasonable suggestion but... Given the wide differences between airports, runways and taxiway layouts - to say nothing of the differences between aircraft types, I think it would be nearly impossible to make this a formal 'rule.'
I rather like response #3 from wannabe777 and keeping all engines burning at least until clear of the last active runway. SOP or not, his practice sounds like a very good choice. At the end of the day, the ticket sellers and the cabin crews do compete - a lot. and it ends behind that semi-secure door. Forward of said door it is still safe flying and noting else. Good airmanship and courtesy are important, there is no company or brand competition at the pointy end. Safety and courtesy are the operative practices. Period. With apologies for the sermon, we already know this stuff. Once in a while, someone forgets, but I think most readers of this space include such things in their daily practices.
**If anyone** comes up with a citation for the SE rule at LHR, I'd sure like to see it! (Now long retired, it make no difference to me, but again, I've never heard of such a rule. Anyone?