The Government has been accused of "soft-pedalling" over the death penalty and seeming to make trade more important than human rights.
The charge by Amnesty International UK's director Kate Allen comes as the human rights organisation released figures showing that at least 1,634 people were executed in 2015, a rise of 54% on the year before.
Despite being the highest number Amnesty has recorded since 1989, this total does not include China, where thousands were likely to have been executed but where the death penalty is a state secret.
The figures - contained in the report Death Sentences and Executions in 2015 - show that the top five executioners in the world in 2015 were China, Iran, Pakistan, Saudi Arabia and the USA.
This "profoundly disturbing" surge in executions was largely fuelled by big increases in Iran, Pakistan and Saudi Arabia, Amnesty International reported.
Amnesty International's fears have been raised just hours after MPs on the Commons Foreign Affairs Select Committee said there is "plainly a perception" the Government is prioritising trade and security with China, Saudi Arabia and Bahrain above human rights.
Ms Allen said: "Like the Foreign Affairs Committee yesterday, we're worried that the Government has started soft-pedalling over foreign countries' use of the death penalty, preferring to prioritise trade with countries like China, Saudi Arabia or Pakistan.
"Until recently the UK's policy of seeking global abolition of capital punishment had a clear focus and strategy. Now the death penalty's been thrown into the pot with other concerns and it's much harder to tell whether the Government is prioritising this life-and-death matter.
"If governments in Beijing, Tehran, Islamabad and Riyadh aren't hearing about our outrage at executions after torture and unfair trials, then the executioners are going to think they've got a green light to carry on killing.
"We want to see the Foreign Office publishing a clear strategy for its anti-death penalty work at the earliest opportunity."
Amnesty International's secretary general Salil Shetty said: "Iran, Pakistan and Saudi Arabia have all put people to death at unprecedented levels, often after grossly unfair trials."
Last year, the Foreign and Commonweatth Office's most senior civil servant made a frank admission to MPs that human rights "is not one of our top priorities" and that the "prosperity agenda is further up the list".
Ministers deny the issue has been downgraded but a string of trade-focused, red carpet visits to the UK by the leaders of countries with some of the worst records of rights abuses has reinforced the perception of a shift of diplomatic emphasis.
At least 977 people were executed - mostly for drug-related crimes - in Iran in 2015, according to the report. This increase, from approximately 743 in 2014, included at least four people who were under 18 at the time of the crime for which they were convicted, as Iran persists in its stance as one of the world's last executioners of child offenders, Amnesty International said.
At least 326 people were sent to the gallows in Pakistan in 2015 while executions rose by 76 per cent on the previous year in Saudi Arabia, where at least 158 people were killed. Most were beheaded, but firing squads were also used and executed bodies were sometimes displayed in public, it was noted.
The world's death row population stands at a minimum of 20,292 people, according to Amnesty International figures.
Saudi Arabia is the only country to use beheadings and two women - one in the Maldives and one in Saudi Arabia - were sentenced to death by stoning for "adultery". The Maldives conviction and death sentence were later overturned while the Saudi Arabian death sentence was later commuted.
Chad, which had not executed anyone for more than a decade, resumed executions and put ten people to death.
The USA executed 28 people - its lowest number of executions for 25 years, while The Republic of Congo, Fiji, Madagascar and Suriname all abolished the death penalty last year.
Human rights minister Baroness Anelay said: "I am deeply troubled by the increase in the number of reported executions in 2015, which was driven by concerning increases in Pakistan, Iran and Saudi Arabia.
"The UK opposes the death penalty in all circumstances and we make our opposition well known at the highest levels to countries which continue to apply it. Our message to them is clear, the death penalty is unjust, outdated and ineffective. It also risks fuelling extremism.
"Despite these concerning figures there has been progress in many countries. It is welcome that in 2015 Fiji, the Republic of Congo, Madagascar and Suriname all abolished the death penalty.
"The Foreign Office will continue to use its diplomatic network to push for progress towards the global abolition of the death penalty."
Maya Foa, of Reprieve, described the rise in executions as "extremely troubling" adding: "It is all the more disturbing, therefore, to see what the Foreign Affairs Select Committee this week described as an 'apparent deprioritisation' of human rights by the UK government.
"Now more than ever, Britain needs to be speaking out against the grave abuses - including mass trials, torture and death sentences handed down to juveniles and political protesters - being committed by its allies."