The victims, brothers working for the self-proclaimed Chechen Republic, formerly part of the Soviet Union, had both been executed, police said.
The men, who have not yet been named, were both shot in the head a number of times with a small-calibre weapon, the Metropolitan Police said yesterday.
Their bodies were found after furniture removal men alerted police about a delivery they had been asked to make to a house in Harrow, north-west London.
The workmen said they had delivered furniture to a penthouse flat in central London at the weekend, then were asked by the flat's two occupants to take a large box to the Harrow address. They were told the box contained antiques.
They left the box in the garage of a house but were concerned about the smell coming from it.
Detectives with a warrant searched the Harrow address and found the decomposing body of a 40-year-old man trussed up in the box. He had been shot three times in the head.
Police kept the penthouse in Bickenhall Street, Marylebone, London, under surveillance and arrested two men as they entered it on Monday. A search of the flat revealed the body of a second man, aged 35, also with wounds to his head, in a bed in a locked bedroom. He also had been shot in the head several times.
Both murder victims were in Britain as advisers to the government of Chechen, a Sunni Muslim state in the Caucasus mountains led by the flamboyant General Djhokar Dudayev. The country, near Georgia, has valuable oil reserves.
Neither had official diplomatic status but they were negotiating several valuable deals with British companies to design and print money, postage stamps and passports for the new republic.
The dead men had lived in the two-storey penthouse since last December.
Terry Catlin, whose company, Bridgestead Estates, manages the mansion block, said the penthouse was sold in December to a foreign company which he believes was registered in South America. It is believed the company paid almost pounds 1m cash for the apartment.
Police confirmed the two men being questioned in custody were Chechen nationals. They admit they have no firm clues about a motive for the killings. A weapon has yet to recovered.
The 1.3 million citizens of the Chechen republic are well-armed and volatile. Russian detectives claim that some of Moscow's most powerful crime gangs are run by Chechen clans and that they are behind most serious crime in the city. They specialise in stealing and reselling foreign cars and spare parts, and controlling prostitution and extortion rackets.Reuse content