By Graham Hiscott Its space station-style structure has loomed over London since 1964, and played host to famous faces just as towering, including Muhammad Ali and Mick Jagger. And now the BT Tower is about to embark on its next defining chapter with plans to turn it into a swanky hotel after being bought for £275million by American chain MCR Hotels. Telecoms giant BT yesterday said advances in technology meant it no longer needed the 620ft landmark, which was commissioned by the General Post Office to handle growth in TV and telephone links across the country. Originally known as the Post Off…