The Marine Accident Investigation Branch has published its report on a collision between a Thames Clippers catamaran and a rigid inflatable boat on the Thames near Blackfriars Bridge last summer.
The MAIB report describes the dramatic episode which took place on the River Thames near Blackfriars Bridge on 1 June 2011 which left the two co-owners of the Morfil rigid inflatable boat in the water after their craft had come into contact with the Sun Clipper catamaran operated by the Thames Clippers company.
Investigators found that the coxswain of Morfil was under the influence of alcohol and the boat was travelling at a "significantly greater" speed than the 12 knot limit set by the Port of London Authority.
The collision, which happened at 11.21pm, occurred after the co-owners of Morfil had visited a pub at St Katharine's Dock before heading back to the boat's mooring at Cadogan Pier.
The report describes how passengers on the Sun Clipper threw lifebuoys to try to rescue the two Morfil crew members. The men, who were not wearing lifejackets, were eventually pulled from the water by RNLI lifeboat crews.
Morfil continued to spin around once its crew had fallen into the river, ricocheting off the stone buttresses of Blackfriars Bridge before eventually coming to rest on the beach on the north side of the bridge.
The MAIB notes that at the time of the accident, Morfil's coxswain is likely to have had at least six units of alcohol in his body, more than double the alcohol limit for motorists and professional mariners.
"It is therefore likely that his decision making and actions were impaired by alcohol," says the MAIB.
The report also notes that "there have been at least 45 fatalities resulting from accidents to pleasure vessels over the last 6 years in which alcohol has been a contributory factor.
"It was extremely fortunate that a further two fatalities did not result from this collision.
"The introduction of an alcohol limit for persons in charge of pleasure vessels was first recommended in the Hayes Report almost 20 years ago.
"Although the provision for such a limit was made in the Railways and Transport Safety Act, 2003, the pertinent subsections of the act have yet to be commenced. The use of byelaws by harbour authorities to deter alcohol consumption on pleasure vessels is largely ineffective.
"A recommendation has been made to the Department for Transport aimed at expediting the enactment of a national alcohol limit to persons in charge of pleasure vessels.
"A recommendation has also been made to the Port of London Authority designed to further enhance the safety of all water users on the River Thames."
The Port of London Authority has welcomed the investigation's findings.
"This is a very good and thorough report into a serious accident which could easily have resulted in fatalities," said a PLA spokesman.
"The report highlights the dangers of speeding vessels in confined and congested waterways; and of alcohol consumption by those in charge of boats, which should be regarded no differently to drink-driving on the roads.
"In this very busy year for London this report goes to the heart of why safety is crucial for all river users at all times.
"We welcome all the MAIB key recommendations and in particular continue to work with the Department for Transport to strengthen the PLA's safety regulations and enforcement."
• The PLA prosecuted Morfil's coxswain, who pleaded guilty to navigating in a manner liable to injure or endanger persons and other vessels before City of London Magistrates and was fined £2,500, with £3366 costs plus a victim surcharge of £15.