Former Director of Public Prosecutions Lord Macdonald of River Glaven also accused British government of assisting the US to carry out the drone strikes by passing on intelligence.
"The Government must come clean over the alleged help it is giving the United States to wage its controversial campaign of drone attacks in Pakistan," Lord Macdonald was quoted by The Times as saying.
He said there was compelling evidence that the Government's secret listening post, GCHQ, had assisted the US in locating al-Qaeda and Taliban chiefs before the strikes.
Lord Macdonald, now a Liberal Democrat peer and chairman of Reprieve, said British ministers could even be forcing some of their own workers to break international law by passing on intelligence and it was likely that ministers had taken a "major decision" to help America with its attacks.
"Such a serious policy risked causing anger against the West and should not be kept secret from the British people," he said. "The evidence is pretty compelling that we are providing that kind of information to the Americans..."
"I've been to Pakistan and I have seen what drone strikes can do," Lord Macdonald said.
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"Innocent people do get killed as a result of misplaced strikes. It is also succeeding in creating a new generation of people with huge resentment against the West, fuelling the kind of terrorism we are trying to fight. The fact this is one-sided, mechanised and robotic gives these strikes a particularly sinister dimension," he said.
The drone strikes have put relations between Washington and Islamabad under intense strain since they began in 2004. Pakistan believes the strikes within its borders violate its national sovereignty and contravene international law.
Figures from the Bureau of Investigative Journalism suggest that 344 strikes have been launched by the US in Pakistan's territory, killing up to 3,300 people. While most were alleged militants, hundreds were innocent civilians.