A Tuck's Oilette by Harry Payne dating from 1906 showing the Bank of England Picquet or Guard entering the Old Lady of Threadneedle Street, in this case they are from the Coldstream Guards. The foot guards had been employed for this duty since 1780 after the Gordon Riots, during which many London buildings were damaged or destroyed; the Bank was extensively damaged during the riots. The duty consisted of an overnight shift of thirteen hours during which the guard secured the vaults containing the nation's reserve of gold bullion. Up until 1963 the Guard marched from either Wellington or Chelsea barracks to the City and the Bank in full ceremonial uniform. flic.kr/p/nktJP8
After 1963 they wore service uniform and were transported by lorry. A Grenadier Guards Officer once told me that when he was commanding the Guard at the end of the night he felt sorry for his men who were due to march back to barracks, so he called up the lorry and transported his men as far as Horse Guards Avenue. They then marched back to Wellington barracks where he was met by his commanding officer who had twigged what he had done and was furious, no port in the mess that evening. Due to increased security at the Bank, CCTV etc and the financial cost of the operation, it was decided to end nearly 200 hundred years of tradition and the last Guard took place on the night of 31st July 1973.
There is an interesting film which is set at the Bank called "The day they robbed the Bank of England" starring Peter O'Toole as the officer commanding the Guard.