The chances of an older vessel surviving a collision on the River Thames have not significantly improved since the Marchioness disaster 30 years ago, the Port of London Authority (PLA) has warned.
Fifty-one young people died when the pleasure boat Marchioness, packed with partygoers, collided with the dredger Bowbelle in central London in the early hours of August 20 1989.
PLA chief executive Robin Mortimer said the tragedy led to a series of safety improvements on the Thames but little has been done to reduce the risk of older boats sinking after a crash.
“The concern we’ve got is that the impact side of the risk is still fairly similar for older vessels because the vessel itself hasn’t changed.”
Flashing lights on bridges and a system for tracking river traffic are among steps taken to reduce crashes on the river since the disaster.
“If all of those measures don’t work effectively and there is a collision then the consequences could still be very serious,” Mr Mortimer said.
The PLA is responsible for overseeing navigational safety on the Thames.
Following a public inquiry into the accident, Lord Justice Clarke published a report in 2001 stating that older boats should not have an open-ended exclusion from modern safety standards.
Modern vessels have several compartments below the water line to reduce the likelihood and speed of them sinking if they start to flood after an accident, but many older boats are not required to survive even minor damage.
Mr Mortimer accepted it is too expensive or impractical for some older vessels to be adapted to meet tougher regulations.
Since January 2010 there have been 35 collisions on the Thames involving vessels built before 1992.
In 2008 a modern boat which suffered an eight-foot gash after crashing into Westminster Bridge stayed afloat as flooding was contained to a single compartment.
Mr Mortimer warned that if the incident featured an older vessel “it potentially would have sunk and there could have been a serious number of casualties”.
Most of those onboard the Marchioness were high flyers from the finance and fashion worlds.
The victims included Francesca Dallaglio, 19, the sister of former England rugby captain Lawrence Dallaglio.
Those who lost their lives will be remembered in a vigil on Monday night.
A procession will leave Southwark Cathedral and make its way to Bankside, close to the accident site.
Survivors and families of the victims will speak at a short service led by the Bishop of Southwark.
Attendees are invited to bring natural petals to throw into the water and carry a candle in a jar.
Pleasure boats and vessels belonging to the police, fire and rescue, the Royal National Lifeboat Institute and the PLA will gather on the river.