An influential US Senate committee is ready to send members to the UK to question British witnesses on the release of Lockerbie bomber Abdelbaset Ali Mohmed Al Megrahi on compassionate grounds, it was revealed.

Senator Robert Menendez revealed the plan after British witnesses including former Justice Secretary Jack Straw, Scottish Justice Secretary Kenny MacAskill and First Minister Alex Salmond turned down requests to attend a hearing of the Senate Foreign Affairs Committee hearing in Washington.

Mr Salmond said he was happy to offer a visiting US senator "the courtesy" of a meeting. But he said there was "no way on Earth" that Scottish ministers would formally give evidence to a committee hearing of a foreign legislature, even if it is held in the UK.

Mr Menendez has been one of the most vocal US politicians calling for an inquiry into the decision to free Megrahi, who returned to a hero's welcome in Libya last year and has now long outlived the three months which he was given to survive terminal cancer when he left Greenock Prison in Scotland.

Mr Menendez on Wednesday accused the British politicians who failed to attend this week's hearing of lacking "courage" and "stonewalling".

And last night he told BBC2's Newsnight: "In addition to making a request for them to come to hearings, we will be... having someone travel to Great Britain and Scotland to interview the individuals and ask questions and get a better understanding of how they came to their decisions."

Mr Menendez said the committee also wanted to talk to outgoing BP chief executive Tony Hayward about what role the company played in lobbying for a prisoner transfer agreement at a time when it was negotiating a multi-million pound oil deal with Libya.

"We are after the truth, and we want all parties to co-operate with the committee," he said.

But Mr Salmond told Newsnight: "We are co-operating with the Senate Foreign Affairs Committee. Its chairman John Kerry has described our response as thoughtful and thorough and we have answered all questions that Senator Menendez has sent to us, with the sole exception of his request to release American Government documents which we can't release because the American Government hasn't given us permission.

"I don't think there is a recorded case in history of a serving American Secretary going to a foreign jurisdiction to give evidence to a committee of another Parliament. That applies to the Chilcot Committee (into the Iraq War), it applies to coroners' inquests in England, it applies to extraordinary rendition and all the other controversies the US has been involved in.

"You shouldn't ask other people to do things that your own Government would never dream of."

He added: "There's an important point of principle here. I am First Minister of Scotland. My ministers and officials are responsible to the Parliament and people of Scotland. They are not - with enormous respect to Senator Menendez - responsible to the American Senate.

"If an American Senator wants to come to Scotland, then the chances are we would extend him the courtesy of a meeting. I do that all the time.

"But there is no way on Earth that the Senate Foreign Affairs Committee is going to hold a hearing in London or in Scotland. It is a point of principle that you are not responsible to a committee of another Parliament, and that would apply wherever that committee is meeting."

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