The Princess Royal was the guest of honour at an unusual event staged at the Tower of London –  the presentation of a barrel of wine to the fortress’ Constable.

Anne watched as the historic “Ceremony of the Constable’s Dues” was held at the former royal residence in the heart of the capital, featuring the ship’s company of HMS Albion – an amphibious transport dock of the Royal Navy.

Lord Houghton, Constable of the Tower of London, was present as was Defence Secretary Ben Wallace.

Historic Royal Palaces, a charity which manages a number of royal premises including the Tower, described the event on its website: “The ‘Dues’ are one of several perks that the Constable of the Tower traditionally enjoyed.

“Every ship that came upstream to the City had to moor at Tower Wharf to unload a portion of its cargo for the Constable.

“Still today, whenever a Royal Naval vessel moors on the Wharf, the Captain must present the Constable with a barrel of wine (the ‘Dues’).

“This is ceremoniously escorted into the Tower by the Yeoman Warders and presented to the Constable on Tower Green.

“Other tariff once extracted from Londoners included any horse, oxen, pigs or sheep that fell off London Bridge.

“The Constable’s Dues has never become just a symbolic ceremony. Once delivered to the Queen’s House the barrel is opened and the wine enjoyed.”