Storming,
You are not wrong. Like me, though, perhaps a little old with a half decent memory. So many commercial planes fancied landing at Northolt instead of lhr that a very large NO with a arrow was painted on a very large gasholder at South Harrow. I'm not sure whether it could be seen in the dark.
back in the 50s there were some scheduled flights to Northolt, so maybe doddery ex-RAF types were simply going where their memory told them......
...and as for some Navigators, I was at farnborough, awaiting a B52 fly-past, when the B 52 decided to fly-past Blackbushe instead.