The UN's special rapporteur on torture has accused Britain of playing Bahrain's "game" by funding its human rights institutions while allowing it to act with "impunity" by not pressuring the kingdom to let him visit.

Juan Méndez, whose 2013 visit was postponed by Bahrain, told BuzzFeed News the kingdom had "played the UK's support to maximum effect". While Méndez does not have legally binding, enforceable powers, the public nature of his reporting could potentially damage the kingdom's standing on the world stage.

"They tell everyone, 'We have an inspectorate of prisons,' but they won't invite me," Méndez said. "The UK should not be a party to it. [Bahrain dismisses its] critics as pawns of Iran. Bahrain considers itself shielded [from scrutiny] due to its relations with Britain and America."

Public demonstrations have been banned in the capital since the Arab Spring, and Amnesty International has said prisoners have been tortured, including being burned with cigarettes and given electric shocks.

Britain is currently offering a "package of technical assistance" to the Middle East kingdom, with £2.1 million allocated for 2015-16 aimed at helping the government reform and for "strengthening human rights and the rule of law".

Among the institutions funded or supported in other forms by Britain are Bahrain's police ombudsman, the group criticised for failing to investigate torturing of a prisoner who has been sentenced to death; and the prison inspectorate, which recently raised eyebrows after allegedly failing to probe torture claims at the kingdom's Jau prison. British Foreign Office sources told BuzzFeed News that despite these setbacks, confidence in these organisations is increasing and they are working more effectively.

The department also funds Bahrain's National Institute for Human Rights (NIHR). In April, an NIHR commissioner tweeted that those who accuse Bahrain's King Hamad bin Isa al-Khalifa of "crimes against the state" should face the death sentence.