Tony Blair’s Government was urged to consider occasionally closing the Thames Barrier in order to allow pageants and parades, newly released files show.

Alex Allan, private secretary to the prime minister in 1997, wrote to Cabinet minister Peter Mandelson two months after New Labour swept to power to float the idea of “making greater use” of the historic but sometimes treacherous waterway.

It followed a conversation Mr Allan had with Sir Brian Shaw, chairman of the Port of London Authority, who suggested closing the Thames Barrier flood defence scheme a couple of days a year for activities.

The proposals, contained within a document prepared by Sir Brian, were disclosed as part of the latest tranche of files released by the National Archives at Kew.

The document suggested a number of possible uses to coincide with the new millennium, and read: “Activities could be arranged to suit the particular locality, such as an Edwardian floating picnic at Richmond, a celebration of Pomp And Circumstance and History in the Pool, and a maritime pageant off Greenwich.

“There would be an opportunity for safe parades of interesting vessels like steamboats, Thames Barges and Dunkirk Little ships, up and down the river, including small pleasure craft which normally find the tidal Thames altogether too inhospitable.

“The movement of craft could build up to a mass assembly in the Pool or at Greenwich, or indeed at both places simultaneously, allowing the craft then to disperse upstream on the flood tide at the end of the Barrier closure period.”

The ideas failed to get past the Thames Barrier and Flood Prevention Act, however, which state that the Barrier can only be closed for a strict number of reasons such as training and testing.

The Environment Agency said the Thames Barrier had been closed 199 times since it became operational in 1982, 108 were to protect against tidal flooding and 91 were to protect against combined tidal/fluvial flooding.