I've just found this site today, so excuse presumption by butting in.
Duty bands are still worn today by the City of London Police (the smallest but best force in London). They are worn on the tunic, which these days only gets used for ceremonials and court. They are coloured red and white, like the dicing on the caps.
During the 1970's their was a belted light-weight tunic worn during the summer months (no shirt sleeve order then). The small band od 'Drivers' attached to the Police Garage had tunics issued without the belt (as the buckle poked the guts whilst seated), and they were also exempt duty bands in case they got entangled in the gear stick or other controls.
Apart from differing from the rest of the country in using red and white the City also have gold numerals, chevrons, pips and crowns etc. They are also unique in not having a Royal Crown on their helmet plates. This relates to the independence of the City of London dating back to the English Civil War: even today, HM The Queen has to officially request permission from the Lord Mayor to enter the City for official functions.
Stephen
(I'll hand this thread back to the Mets to swing their lamps)