LONDON, March 31 — For approximately the fifteenth time this year, an uncredentialed and possibly unstable academic, identified by government officials only as “The Doctor,” averted a potential alien invasion of London, aided only by a handheld device that lit up and made beeping noises.

The Doctor, clad in a business suit and Converse athletic shoes, was most recently sighted at the British Government’s controversial Centre for Intradimensional Research in the former Battersea Power Station, shortly after an experiment in breaching the fabric of space-time threatened to leave the entire planet vulnerable to a race of sentient, malevolent, gaseous creatures known as the Kr’Veel.

As British Army soldiers attempted to engage the creatures, who had already devoured three of the scientists involved in the project, the Doctor was sighted pointing his strange blinky device at various locations on the dimensional gate’s main control console, while muttering intensely to himself. Within minutes, the gate appeared to reverse direction, pulling the rampaging Kr’Veel back to their native dimension amid a sudden howling gale; the Doctor could be seen apparently delivering some kind of bold and triumphant address to the creatures, but his words were inaudible over the wind.

Following the closure of the dimensional gate, and the restoration of calm, the Doctor proceeded to mourn the fallen scientists intensely for a period of roughly twelve seconds, after which, witnesses reported, he began grinning hugely and skipping away over the corpses.

Following the incident, the Doctor, who declined to provide a name, chided Earth — and particularly London — for its careless invitation of alien invasions. “Can’t get a moment’s peace with you lot, can I?” he said. “It’s all, ‘Say, let’s open a gate to another dimension! Can’t be any consequences in that, can there?’ I can’t be everywhere at once, you know. I mean, London’s lovely and all, but what if there had simultaneously been, say, a Dalek incursion in Rio de Janiero? Or a Cybermen attack in Cleveland. Lovely town, Cleveland. Fan-TAS-tic chili dogs. Rock N’ Roll Hall of Fame. Cybermen can’t resist a good Buddy Holly number.”

Embattled Prime Minister Harriet Jones’ office issued a statement praising the courage and quick thinking of the soldiers and scientists involved, but declined requests for interviews related to the Doctor. Political opponents in Parliament say this incident adds to Ms. Jones’ poor security record regarding extraterrestrial threats.

This is only the latest sighting of the mysterious Doctor and his odd, noisy little device. Various men answering to the title have been definitively reported as far back as the 1960s, with less reliable reports dating back further still. After a lull of more than a decade, the most recent Doctor has been seen in London with increasing frequency in the past few years, sometimes with a young blonde woman, often at the site of various disasters or alien incursions. He is reported to have played a key role in 2005’s “Christmas Invasion,” and the May 2005 “Battle of Canary Wharf,” in which British Army troops engaged invading cyborg marauders.

Gwen Cooper, acting head of the government’s Cardiff-based Torchwood Institute, an agency created to catalog human contact with alien phenomena, declined comment on the Doctor’s latest appearance. “Sorry, sorry,” Ms. Cooper said by phone. “We’re a bit short-staffed at the moment, and the place is a mess. Say, this Doctor — there wasn’t an American bloke with him, by any chance? Braces, long coat, kind of raffishly charming in a pansexual sort of way?”

“His behavior suggests a dangerously unstable individual,” said Fox Mulder, a former FBI profiler who now works as a private consultant to law enforcement. “Witnesses report that he seems to swing wildly between elation and heartbreak, which could be a sign of post-traumatic stress. At any rate, I wouldn’t trust anyone exhibiting those traits. No matter how cool their funky blinky device.”

Between the recent Shining Dawn terrorist bombings and alien incursions, Londoners have grown increasingly nervous about security threats in the past few years. In a curious footnote, police report that the Doctor’s appearances tend to correlate with a rise in reported sightings of traditional blue police call boxes, though none have been in service since the 1950s.