Foreign Secretary David Miliband was scheduled to address Parliament over the issue, following an investigation into the use of 12 fake U.K. passports in the incident.
Britain's Foreign Office would not provide any details of Miliband's statement in advance.
"The Foreign Secretary will make a statement to the House of the Commons this afternoon," a spokeswoman said, on customary condition of anonymity in line with policy.
However, the UK official, speaking on condition of anonymity because he was not authorized to comment ahead of the statement, confirmed one Israeli diplomat will be expelled.
Israel's foreign ministry confirmed that the country's ambassador to Britain Ron Prosor was called to London's Foreign Office on Monday for talks, but declined to provide further details. There is no suggestion the ambassador himself would expelled, the diplomat ordered out of Britain is expected to be a lower-ranking official.
"We can neither confirm nor deny," a diplomat had been expelled, said a spokesman at Israel's London Embassy, speaking on condition of anonymity because he was not authorized to speak to the media on the issue.
Dubai authorities have accused Israel's Mossad spy agency of being behind the Jan 20. slaying of Mahmoud al-Mabhouh in a luxury hotel room, and have identified at least 26 suspects of an alleged hit squad that traveled to Dubai on fake identities and forged European and Australian passports.
Interpol has unveiled a wanted list of 27 people in connection with the slaying. Israel has neither confirmed nor denied any involvement in al-Mabhouh's killing.
At least 15 of the names used by the suspected killers match those of Israeli citizens who are dual nationals of Western countries - including eight Israeli-British dual nationals. All have denied involvement, saying their identities were stolen.
Shortly after he was named as one of the British suspects, dual national Melvyn Adam Mildiner told The Associated Press that he thought he was picked because "I don't have a Jewish-sounding name."
It is suspected Mossad specifically targeted the identities of dual nationals. It is relatively easy for British Jews - and Jews from other nations - to qualify for Israeli passports if they meet the basic requirements set out by the Israeli government. It remains relatively commonplace for people to carry valid passports from both nations.
In a recent speech, Eliza Manningham-Buller - the ex-head of Britain's MI5 - said forged British passports had previously been used by the same country behind the Dubai slaying, though she declined to specifically name Israel.
Diplomatic expulsions are a rare sanction against foreign governments. Britain kicked out four Russian diplomats in 2007 over the country's refusal to extradite to London a suspect in the poisoning death of Alexander Litvinenko.
The country's Serious and Organized Crime Agency has conducted an inquiry into the use of forged British passports, but is not involved in wider inquiries by Dubai police into the killing.
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Associated Press Writers Raphael G. Satter and Gregory Katz, in London and Aron Heller, in Jerusalem, contributed to this report
