Had a look on Flightradar24 to see what was happening in the UK at around 4am their time & the screen was almost blank apart from this one flight from Bridgetown in the Bahamas to Birmingham.    Birmingham had been closed due to snow but obviously there was some chance it would re-open in time for this flight.    No-go they had to divert to Gatwick after making several circles in the sky South of Birmingham.    I did a screen grab.    While this was going on the air traffic controllers at Heathrow only had about three planes coming their way but I guess Gatwick was the preferred choice.   Not an ideal way for people to finish their holiday!