BA749 Basel - LHR Squawks 7700 and diverts to Stansted
 

I would expect this to be fuel related after a number of orbits and then a change of stack for more.

Weather in NW London has been horrid for the last half an hour - thunder and hail - and looking at FR24 Heathrow stopped any approaches or departures for a time.

But it was only one full loop in the stack and then one orbit - doesn't seem an unreasonable delay to expect when approaching LHR...

And now the 685 from Innsbruck is going the same way!

Are all these diversions part of the calculation for the environmental impact of a third runway...?

I'll defer to Heathrow Tower's knowledge here, but I reckon running out of fuel would be a good underlying reason.

1990, AV 52. A 707. The NTSB determined that the crash occurred due to the flight crew failing to properly declare a fuel emergency.

For all we know there might have been an urgent medical issue on board in addition to everything else...

Just to re-iterate the OP noted the plane broke off on final approach into LHR, having flown a short holding pattern. Not a typical place to declare a fuel emergency and fly off to a more distant airport.

Where was this plane relative to the lightning strike on the 777 inbound from BOS ?

Fair enough to some of the responses but aren't people missing the point that the craft was already on final approach? As mentioned by Oxon Flyer why would an aircraft fly to a more distant airport if on final approach and facing a fuel shortage?

I'm more interested than challenging to be honest.

Or, possibly, it didn't like the look of whatever weather was between it and the field, and therefore broke off the approach, there was no assurance of getting around the "circuit" in the circumstances to be able to approach LHR again and land within the fuel available, and so it had to divert to another field at that point - STN was OK for weather but far enough away that an emergency call was required because of the expected fuel state on landing there. And perhaps the weather was looking different for BA238 given the time interval, but in the end there was still something in the same bit of weather that produced the nasty that hit it.

Or, in other words, we can all speculate as much as we like without shedding any light.

I’ll defer to more knowledgable sources but IF this were a fuel emergency then this does NOT mean the aircraft is ‘running out of fuel’. I think flight crew are required to declare an emergency if they can’t be sure they will arrive at their alternate airport without eating into final reserve fuel.

This video shows how some changes in estimated holding time can cause one to have to make a decision as to whether or not to divert:

just to clarify BA749 was over Brixton when it decided to divert ... closer to central London then Richmond Park, but not what i would call central London !

I was on this flight. We were diverted apparently as a precaution due to the reports from other flights ahead of us.
After landing at Stansted there was some discussion about whether to disembark (some pax living in the area were particularly keen to do so).
We were on the ground for a couple of hours before flying on to LHR (15 mins wheels up to wheels down).

Wrt refuelling, we were delayed departing Innsbruck to refuel. We then had to refuel again at Stansted.
Free soft drinks were dispensed on board during the delay.

There was much discussion on board about compensation for the eventual 3hr or so delay in landing at T5, but presumed by all that would be rejected due to it being extreme weather-related.

STN to LHR. Depending on the route that's shorter than a ZRH-BSL flight I've taken. They're both about 55 miles.