Clue: Worthy at one time to go round square to 9 with banners (11)
Answer: ALDERMASTON
Explanation: Definition: 9 with banners
S TO in ALDERMAN – a worthy "at one time" because, as I didn't realise, this office was abolished in 1974 (or 1978 in London). The marchers at Aldermaston not only carried actual banners, but wanted to **Ban** the Bomb.