The transmitter is London's third-tallest structure, and from its construction in the 1950s until the completion of One Canada Square at Canary Wharf in 1991 it was the tallest in London, standing as it does 219 metres tall.
Whilst it is visible across South and Central London, it isn't really until you get up close that you get the real scale of the thing. When your author visited for the first time back in the summer, he was amazed. He is only sorry that at this time of year he can't guarantee the weather, and that you will be able to see the top today.
For more, see http://en.wikipedia.org/wiki/Crystal_Palace_transmitting_station