Natasha's doors were all in her mind, memory aids developed to help with tasks including memorising a 2,000-digit number, a list of 500 words, 100 names and faces and the orders of 12 packs of cards. Pictures, binary numbers and an original poem by Ted Hughes added to the variety of memory skills. Mr O'Brien, 35, who holds the world record for memorising the order of a single pack of cards in 55 seconds, has devised a mnemonic system in which each becomes first a pair of initials, then a person. So the three of clubs, for example, becomes CC, Charlie Chaplin and a twirling cane. Leave your 52 people in 52 locations on a well-practised route and you can pick them all up in the right order. Unless, like Natasha, you mentally rush past the door half-way up the stairs.
Like chess or train spotting, memory at this level seems to be a game for the dedicated specialist with little transferability to real life, though Creighton Carvello, a former champion who finished fourth this year, believes it was useful for him to memorise 5,000 telephone numbers from the Yellow Pages.
When the competition was over, the contestants were faced with the problem of clearing the detritus of random numbers, cards, words, pictures and Charlie Chaplin from their strained minds. Dominic O'Brien has a technique for that too: 'I put them away on a mental video,' he said, with a gesture of removing something from his head and placing it behind him.