While history offers no direct comparison to the al-Megrahi affair — a man convicted of killing 270 people would have been executed long before any release on compassionate grounds — the US has long taken an interest in how Britain treats terrorists.

In contrast to the case of the Lockerbie bomber, US public and political opinion often interceded to get IRA terrorists released early. While Americans salute the memory of Senator Edward Kennedy, they may recall that considerate treatment of terrorists held in Britain was among the themes of his famous compassion.

Such a close interest did not just coincide with the 30-year Troubles in Northern Ireland. In the early 1880s transatlantic relations were especially soured by London’s annoyance at US attitudes to the perpetrators of Fenian outrages on the British mainland.

Ministers in Gladstone’s Cabinet were incensed that their counterparts in Washington were not prepared to crack down on the terrorist cells operating from America or to extradite their ringleaders for trial in Britain.

Instead, undisguised fund-raising for bomb-making was justified on the grounds of US freedom of speech. The authorities even refused to act when a British-bound secret consignment of dynamite was discovered with paperwork traceable to the US-based mastermind of the terror campaign, Jeremiah O’Donovan Rossa.

That double standards operated was evident from the attitude of the US Secretary of State, James G. Blaine, who assured Britain’s Minister to the United States, Edward Thornton, that if any Americans were killed in the terror campaign, the “Irish would be exterminated”.

Naturally, the terrorists had more sense than to blow up Americans. Britons, however, were fair game and as indiscriminate bombing spread mayhem across British cities so some of the alleged perpetrators found themselves in British jails. At least a dozen were US citizens. In 1882 the State Department interceded on their behalf. Those deemed not directly culpable were released on condition they left the British Isles.

Although the US President, Chester Arthur, was openly sympathetic to Britain’s predicament, congressmen dependent on the Irish vote thundered about a British legal system apparently beyond “the pale of humanity” whose failure to treat with justice incarcerated US citizens could prove grounds for a declaration of war.

This was windy rhetoric. Nevertheless, while successive presidents supported efforts to strengthen laws against Irish-American bomb-traffickers, Congress repeatedly blocked the legislation until 1909. Further intervention by the Irish lobby in Congress ensured that destruction of property and “malicious injury” to persons were excluded as grounds for extradition to Britain until 1931.

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