The Marchioness disaster occurred on the River Thames in London in the early hours of 20 August 1989. The pleasure boat Marchioness sank after being run down by the dredger Bowbelle, near Cannon Street Railway Bridge. There were 131 people on the Marchioness. Some were members of the crew, some were catering staff and others were guests at a private birthday party. Fifty-one of them drowned. The Marchioness was built in 1923 and in 1940 was one of the little ships of Dunkirk. 
The party was organised by photographer agent Jonathan Phang to celebrate the 26th birthday of Antonio de Vasconcellos, who worked in a merchant bank. The pair were good friends and business partners in a photographic agency. Of Portuguese family background, Vasconcellos had studied Economics at Cambridge University.
Phang organised a three-part celebration: an eight-person dinner in a flat on Meard Street (only two of the diners survived); a birthday cake and champagne celebration for a group of 30 at the flat; and the party on the Marchioness. Many of those at the party were also in their twenties; some were former student friends and others worked in the fashion industry. The dead included Francesca Dallaglio, older sister of future England national rugby union captain Lawrence Dallaglio, and the skipper of the Marchioness, Stephen Faldo, father of reality TV star Jeff Brazier.
In the initial instant of collision the anchor of the Bowbelle cut through the side of the Marchioness. The Marchioness then rolled over and quickly filled with water, while being pushed under by the Bowbelle. As the Marchioness capsized, her entire superstructure became detached. The formal investigation put the time elapsed, from the instant of collision at 1.46 a.m. to complete immersion, at close to 30 seconds. Witnesses quoted in that investigation described the Bowbelle as "hitting it [the Marchioness] in about its centre then (mounting) it, pushing it under the water like a toy boat." Of the deceased, 24 were recovered from the sunken hull. The majority of the survivors had been on the upper decks at the time of the collision.
The disaster was found by the Marine Accident Investigation Branch to have been caused by the poor visibility from each ship's wheelhouse, the fact that both vessels were using the centre of the river and the lack of clear instructions to the lookout at the bow of the Bowbelle. In 1991, the skipper of the Bowbelle, Douglas Henderson, was tried for failing to keep a proper look-out but, after two juries were deadlocked, he was formally acquitted. A Coroner's inquest on 7 April 1995 found the victims had been unlawfully killed.
Following pressure from the Marchioness Action Group, whose publicity front had been handled by photographer and party attendee Ian Philpott, on 14 February 2000, John Prescott as Secretary of State for the Environment, Transport and the Regions ordered a formal investigation into the circumstances of the collision, to be chaired by Lord Justice Clarke. Lord Clarke's report blamed poor lookouts on both vessels for the collision and criticised the owners and managers of both vessels for failing to instruct and monitor their crews in proper fashion.
In 2001 an inquiry by the Maritime and Coastguard Agency into the competence and behaviour of Captain Henderson concluded that he should be allowed to keep his master's certificate as he met all the service and medical fitness requirements. However, they "strongly deprecated" his conduct in drinking 5 pints of lager in the afternoon prior to the accident and for his admission that he had forged some signatures on certificates and testimonials in order to obtain his master mariner certificate of competency in 1988. Also in 2001, the Royal Humane Society made 19 bravery awards to people involved in rescues at the Marchioness sinking.
Subsequent to recommendations made in the Clarke report relating to the improvement of river safety, the Government asked the Maritime and Coastguard Agency, the Port of London Authority and the Royal National Lifeboat Institution (RNLI) to work together to set up a dedicated Search and Rescue service for the tidal River Thames. Consequently, on 2 January 2002, the RNLI set up four lifeboat stations, at Gravesend, Tower Pier, Chiswick Pier and Teddington.
Seven years after the disaster, the Bowbelle was also lost. Having been sold to a Madeiran dredging company and renamed Bom Rei, she split in half and sank on 25 March 1996 off the coast of Ponta do Sol, Madeira. The Tubarao Madeira Diving Organisation discovered the wreck six months after it sank. The wreck is still in good condition and offers refuge to a varied range of fish and marine life. After only a short time, marine plants grew in abundance on the wreck and the boat has become an attraction for divers.
Not far from the site of the disaster, a memorial to the victims can be found in the nave of Southwark Cathedral, where every year a service of remembrance is held for those who lost their lives.
A drama about the events surrounding the disaster, filmed by ITV Productions in association with Leeds-based Chameleon TV, was scheduled for broadcast on ITV in late 2007. However, speaking at the Edinburgh International Television Festival on 25 August 2007, former ITV Director of Drama Nick Elliot confirmed that the drama would not be shown "in its present form", though it has since been shown on French TV. Relatives of some of those killed in the disaster had previously asked ITV not to broadcast the programme, although others thought it "crucial" that it be broadcast, "an excellent adaptation of the full horror of what happened."
In 2011 survivor Magda Allani published a personal account of the sinking and events surrounding it, Dark Waters - Chronicle of a Story Untold, gaining some substantial UK media coverage.
English law provides no compensation for fatal accidents unless financial dependence at the time of death can be proven. In most cases, the victims' families received little more than the cost of the funeral. Civil claims for compensation were brought on behalf of the victims’ families, the amounts received ranged between £3,000 and £190,000. This is due to the fact that many of those killed were young, single, without dependents and had no established careers.
Twenty years on, various acts of remembrance were organised: the Coastguard placed 51 roses in the Thames, near to the site of the disaster. At Southwark Cathedral, the names of the victims were read at both Eucharists on 20 August 2009. Survivors and those who lost loved ones attended a service of choral evensong, sung by the Southwark Cathedral Merbecke Choir. The names of all 51 people who died in the tragedy were read out and two wreaths—one for the survivors, one for the dead—were laid at the Marchioness memorial within the cathedral. A documentary aired on BBC One in October 2009 was called "The Marchioness: A Survivor's Story"; it followed survivor Jonathan Phang's efforts to come to terms with the disaster.
- "Girl's parents lose Marchioness case". The Independent. 2 May 1996.
- "Lawrence Dallaglio moves on with no regrets". Daily Telegraph. 10 November 2007.
- Fletcher, Damien (October 22, 2004). "Farm winner Jeff's real dad was captain of disaster boat." Daily Mirror.
- Formal investigation report
- "Bowbelle skipper keeps his licence". BBC News. 3 December 2001. Retrieved 2007-08-26.
- "Wrecks". 3 December 2001. Retrieved 2010-11-13.
- Martin, Nicole (24 August 2004). "Marchioness families ask ITV to drop drama". The Daily Telegraph (London). Retrieved 2007-08-26.
- "ITV axes 'insensitive' docu-drama". BBC News. 26 August 2007. Retrieved 2007-08-28.
- Allani, Magda. "£1bn mystery of the Marchioness: Magda Allani survived the disaster 22 years ago. Now she asks whether her tormented friend Antonio held the key to the tragedy". Daily Mail (London).
- Louise Christian (12 April 1995 ) "Letter: Compensation for loss of young lives", The Independent
- Dixon, Rob (01 July 2009). "Marchioness Riverboat Disaster". Sheffield: Irwin Mitchell. Retrieved 10 July 2013.
- "Marchioness boat disaster marked". BBC News. 20 August 2009. Retrieved 2009-09-01.
- "Marchioness Anniversary Information, Southwark Cathedral". Southwark Cathedral. 2009-08-20. Retrieved 2009-09-01.
- Phang, Jonathan (October 10, 2009). Life after the Marchioness. The Times.
- Formal Investigation Report into the disaster[dead link]
- Details of the memorial in Southwark Cathedral
- BBC On This Day 20 August 1989 Marchioness river crash kills 30
- Marchioness Action Group
- Obituary Eileen Dallaglio, Founder Marchioness Action Group