This is the 'famous' White Door or Millionaire's Door - a short cut into the Concorde Room, the lounge for passengers with a ticket in First Class (and very top level BAEC card holders - GGL and Premier). It allows you to access the lounge without having to traipse through the terminal or past the shops. BA reportedly paid HAL a large sum of money for this access as it removes high spending customers from the temptation of the luxury mall beneath!

Hang around outside for a minute and you will observe a constant stream of travellers attempting to use it as a short cut, or a blag their way into the Concorde Room by arguing/charming/berating the door keeper. It must be one of the most thankless jobs in the terminal so I am always extra nice to them.

It is almost hallowed in these circles but in reality is a little corridor with a fire exit and a console table with flowers. Still nice to use though and I still remember the thrill of first using it. It's usefulness has been majorly downgraded with the advent of the First Wing (leading passengers directly into Galleries First where they cross over) but it is indeed convenient for First Class passengers who need to get to Boots