The equivocal statement has fuelled suspicions that Britain is turning a blind eye to practices by its allies that many international lawyers believe are illegal.
Holding mock executions is banned in international law, yet simulated drowning is specifically intended to persuade subjects that they are about to die.
Known as "waterboarding," forms of simulated drowning have been used to torment prisoners since the Middle Ages. Victims experience an automatic gag reflex and acute terror, quickly and inevitably pleading for the ordeal to end.
In a written parliamentary exchange, the Foreign Office was asked whether "the infliction of simulated drowning falls within the definition of torture or cruel and inhumane treatment used by the government for the purposes of international law."
Replying, Ian Pearson, a junior Foreign Office minister, gave what some saw as a vague answer. "Whether the conduct described constitutes torture or cruel, inhumane or degrading treatment or punishment for the purposes of the UN Convention Against Torture would depend on all the circumstances of the case," Mr Pearson wrote.
Waterboarding is one of the "Enhanced Interrogation Techniques" that US intelligence officers are said to use against suspected international terrorists.
The CIA version of the technique sees the subject strapped to a board, feet raised. Cellophane is wrapped over the nose and mouth and water is poured over the head.
The technique has since been used on senior al-Qaeda figures in US custody, intelligence sources say. US officials have never denied those claims.
There is no suggestion that British military or intelligence officers have used waterboarding directly against prisoners.
Human rights groups yesterday condemned the Foreign Office's ambiguous legal position on simulated drowning.
James Welch, the legal director of Liberty, said Mr Pearson's answer suggests ministers are ignoring international treaty obligations. "It is incredible that a government minister, mindful of our obligations under the European Convention on Human Rights, UN Convention Against Torture and International Covenant on Civil and Political Rights, could possibly consider that holding someone under water with the intention of making them think they were going to drown was anything but torture," he said.
Kate Allen, Amnesty International's UK director, said the government must take a much clearer position against techniques like waterboarding.
"Instead of equivocating the government should be clearly condemning all forms of torture, including partial drowning, death threats, sensory deprivation and indeed all forms of cruel, inhuman or degrading treatment," she said.