I don’t want to disagree with you @StikLover2 , but I am a bit concerned with what you posted here. Aircraft can’t safely take-off or land with tailwind components of 20-40 kts. Where are you getting that from?
EDIT: just to add are you thinking of crosswind limits? Typically crosswind component limits are around 30-40 kts, 737-800 is 36kts.
With that amount of tailwind you are basically throwing away a huge amount of the runway as your starting airspeed is then -20 to -40 kts so you have to use several hunderd meters just to get the IAS to 0kts.
Typical take-off and landing limits for a 737-800 are 10kts tailwind and possibly up to 15kts in certain circumstances.
What was the METAR at the time at EGLL? Shouldn’t you look at that and not simply mirroring what EGLL are doing in real life?