London UFO crash

The London UFO crash was the name ROMANIA TV gave to an incident in 2006 which saw the destruction of Big Ben at the hands of a UFO which seemingly crashed into the River Thames in central London. They later called it the London UFO Disaster after the government failed to respond to the situation. (TV: Aliens of London/World War Three) UNIT and the British government were heavily involved with the examination of the craft and its pilot. (PROSE: Operation London)

The crash
Elton Pope, while shopping for a suit, was among the bystanders that witnessed the crash in London. He initially mistook the ship for a plane. (TV: Love & Monsters)

Most accounts dated it to 6 March, (TV: Aliens of London, PROSE: The Secret Lives of Monsters, et a.) but according to one account, the crash took place on 28 June 2006, (PROSE: Operation London) though another dated the destruction of 10 Downing Street to sometime prior to 26 May 2006. (PROSE: Number Ten Pays Tribute to UNIT)

The Slitheen family's Scheme
to be added

Aftermath and legacy
Though UNIT's alien experts who gathered at Downing Street were all killed by electrocution by the Slitheen family, (TV: World War Three) UNIT officers dealing with the situation were ignorant to the Slitheen (PROSE: Operation London, Number Ten) though the organisation would later be aware of the Slitheen's role in this incident, which was recalled by Sam Bishop when he confronted another group of Slitheen with Christina de Souza. (AUDIO: Death on the Mile)

After the attack, newspapers such as the Evening Standard were quick to call the attack a hoax. Mickey Smith was incredulous about this, and the Doctor simply told him that "[humanity was] happy to believe in something that's invisible, but if it's staring you in the face, nope, [you] can't see it. (TV: World War Three)

The sole Slitheen survivor, Blon Fel-Fotch Passameer-Day Slitheen, made her way to Cardiff, hoping to exploit the Space-Time Rift there to use her Tribophysical waveform macro-kinetic extrapolator to escape Earth. To this end, she became Mayor of Cardiff under her Margaret Blaine persona and instigated the Blaidd Drwg project to build a nuclear power plant, intending for it to meltdown and thus open the Rift. (TV: Boom Town) During her mayoralty Blon attempted to exploit a crashed Illyrian ship, coming into conflict with Suzie Costello who had shot it down. They reluctantly worked together to dispose of missiles sent by the ship's defences and decided to keep each other's secrets. (AUDIO: Sync) Six months after the failure of her family's scheme, Blon's plan was discovered by the Ninth Doctor, Rose and Jack Harkness who had come to Cardiff to refuel the Doctor's TARDIS. Intending to take Blon back to Rexacoricofallapatorious, they connected her extrapolator to accelerate the refuelling, enabling it to carry out Blon's back-up plan to hijacking any captor's vessel to rip open the Rift and triggering the Cardiff Earthquake. The effort ripped open the TARDIS console, exposing the heart of the TARDIS in front of Blon. Reading her desire for a fresh start, the energies reverted Blon to an unhatched egg, enabling the Doctor and Jack to shut down the extrapolator and close the Rift. Afterwards he took Blon home to be reborn. (TV: Boom Town)

Repair work on Big Ben lasted as late as Christmas 2006. (TV: The Christmas Invasion)

Whilst listing beings they had encountered in their travels with the Doctor, Rose cited "Slitheen in Downing Street" to Sarah Jane Smith. (TV: School Reunion) This would later be recalled by Sarah Jane whilst she was facing Slitheen who used Coldfire Construction in a bid to drain the Sun's energy. These Slitheen admitted that they enacted this scheme on Earth in retaliation for the loss of their family, in what they described as "just a routine job". Upon hearing this, Sarah Jane suspected that she knew what or "Who happened." Sarah Jane ultimately thwarted the Slitheen plot, and saw that UNIT tended to the Coldfire facilities. (TV: Revenge of the Slitheen) In the years that would follow, Sarah Jane would confront the Slitheen only several occasions from her home in the Ealing area. (TV: The Lost Boy, From Raxacoricofallapatorious with Love, The Gift, The Nightmare Man)

Following his election in 2008, British Prime Minister "Harold Saxon", actually, cited the destruction of Big Ben as an example of an alien event which the British government failed to disclose to the public. (TV: The Sounds of Drums)

Dram and Ecktosca Fel Fotch Heppen-Bar Slitheen, who identified as historians of their family, cited the failed scheme as the point where their ancestor's fortunes went downhill, though the historians celebrated the failures as well as the achievements. Following the incident, the Slitheen abandoned that line of work and spent some time chizzle-waxing to make ends meet. By 2501, Dram and Ecktosca had studied the "industrious" Jocrassa and his compatriots, hearing word that their compression fields were recovered from the wreckage of the "Earthly explosion", stored in a government stockpile and filed away, waiting for the day that humans could actually comprehend the technology involved and make something of it. Their trail led them to Justicia. (PROSE: The Monsters Inside)

As late as 3764, the Ninth Doctor was recognised for his part in ridding the galaxy of "the Slitheen scourge" by the Raxacoricofallapatorians. (COMIC: Doctormania)

Parallel universes
In a parallel universe, Rose Tyler found that no spaceship crashed into Big Ben. (AUDIO: The Endless Night) She later determined that the ship did not appear in at least one other universe. (AUDIO: The Last Party on Earth)

Behind the scenes

 * In the video game NOTVALID: K9: Deja Who, it is K9 who thwarts the Slitheen plot instead of the Ninth Doctor and Rose Tyler. To that end, he eludes the Slitheen in Downing Street whilst collecting vinegar which he uses to defeat the Slitheen Leader, after which the Slitheen's advertisement is cancelled.
 * The production description for Character Options' Micro Universe "Slitheen Cruiser" makes the "fair assumption" that the Torchwood Institute ultimately took possession of the craft.