The Foreign Office minister, Anthony Lloyd, said yesterday he was "very concerned" and would be "urgently contacting our [European Union] partners" to co-ordinate a response.
At the height of the row over shipments of arms to Sierra Leone earlier this year, the Prime Minister dismissed the apparent breach of United Nations and EU sanctions as a "hoo-ha". "Let's not forget that both the UN and the UK were trying to help a democratically elected regime," Mr Blair said.
Those sentenced to hang by the government of President Ahmed Tejan Kabbah include Hilton Fyle, a well-known former BBC World Service presenter for the African service, Felix George, the former head of the West African country's Broadcasting Corporation, a newspaper editor, Ibrahim Ben Kargbo, and a radio journalist, Olivia Mensah, who has given birth to a son in prison since her arrest.
Friends and family members of the convicts wept as they were led from the court in the capital, Freetown. Mr Kargbo said: "We know we are going to die. But this is a pointer to all decent citizens that they, too, could be here [sentenced to death] one day."
Mr Lloyd said he intended to speak to President Kabbah "as soon as possible". He said Britain would "make clear to the government of Sierra Leone the need for them to pay heed to human rights, due process and international norms".
The condemned have 21 days to appeal.
The verdicts have drawn protests from the Paris-based Reporters sans Frontieres and the human rights body Amnesty International. The 16 are seen as apologists for the brutal military regime of Major Johnny Komora, which seized power in May 1997, but hanging is viewed as an absurdly disproportionate punishment.
The army coup in the former British colony became politically controversial in Britain this year because of the role of Sandline International, a British firm, which supplied the Nigerian-led West African force that ousted Major Komora. Sandline said the Foreign Office gave it permission to intervene, despite a UN embargo on supplying arms to either side.
"The constant refrain from government ministers was, 'OK, things may not have been well handled here, but in essence, the good guys won'," Menzies Campbell, foreign affairs spokesman for the Liberal Democrats, told BBC Radio 4 yesterday. "It will take something of the shine off the proposition that the 'good guys' won if one of the actions of the good guys is to execute journalists."
Anthony Goldman, of the Economist Intelligence Unit, said the sentences showed that the "ethical" foreign policy of the Foreign Secretary, Robin Cook, was coming unstuck. "An ill-advised policy has now come home to roost. Since [the military] were ousted, there's simply been an escalation of fighting and terrible atrocities," he said.
Critics also complain that President Kabbah's restoration has turned Sierra Leone into a department of Nigeria. Some 10,000 Nigerian troops patrol the capital as part of the West African peacekeeping force. Key ministries, including defence, are also in the hands of Nigerians. "We have replaced an unpleasant military government with Nigerian occupation," Mr Goldman added. "That is the mess British policy has created."
Having publicly committed itself to President Kabbah's government, Mr Blair's influence now faces a very public test as Britain tries to get the death sentences commuted.
The International Bar Association, meanwhile, said the Freetown authorities had done their best in appalling circumstances to provide fair trials. "The whole infrastructure of the country has been destroyed, there are very few lawyers and they are working from ancient law books," said Paul Hoddinott, the IBA executive director. "We have been active in raising objections [during the trials] and they have been acknowledged."
More than 60 civilians are standing trial, and 38 junta soldiers are facing a court martial.