British ministers have acted like overexcited cheerleaders for Bahrain’s woefully inadequate human rights reforms, Amnesty International has said, ahead of an expected visit next month by Theresa May on the sidelines of the annual Gulf Cooperation Council summit.

Ministers ought to be confronting the awkward reality that the institutions set up in Bahrain with UK support “are seriously flawed and widely seen as a PR exercises”, Amnesty said.

The report, based on 90 interviews with Bahraini human rights activists, said it is “utterly disingenuous” of the British government to pretend it is delivering substantial human rights reform in Bahrain.

There is controversy over the value and independence of two UK-supported human rights institutions. Britain also has longstanding military links with Bahrain and is establishing a new military base in the kingdom. The Foreign Office said the two institutions show the government in Manama is willing to respond to western pressure.

The bodies, the ombudsman of the ministry of interior and the special investigations unit within the public prosecution, were established in 2012 following a fierce crackdown by the Bahraini government on protests the previous year.

The then foreign secretary Philip Hammond said Bahrain had been making significant reform, telling the House of Commons it was “a country which is travelling in the right direction”.

However, Amnesty said the special investigations unit has failed to take prompt action to protect detainees from torture, investigate their allegations effectively or ensure their access to medical care.

It pointed out that although it was obvious Hussain Jawad, a prominent Bahraini human rights activist, was at risk of torture following his arrest in February 2015, the ombudsman’s office “failed to carry out a prompt visit to check the conditions of his detention”.

Jawad later said he was blindfolded, beaten with his hands cuffed behind his back and threatened with sexual abuse in order to extract a confession.

Amnesty also said the ombudsman’s office delayed an investigation for two years into the torture allegations of Mohamed Ramadhan, an airport security guard sentenced to death after being convicted of involvement in a bomb attack, despite receiving information from his family and an international NGO.

The special investigations unit has prosecuted 93 members of the security forces, but only 15 low-ranking officials have been convicted, Amnesty noted. No senior officers or officials who oversaw the serious human rights violations during the 2011 uprising have faced prosecution.

Out of nearly 200 cases Amnesty has recorded since the uprising, fewer than 45 have been referred to trial. The organisation pointed out that neither human rights body has gained the public’s trust, partly as a result of a perceived lack of independence and impartiality.

Both are viewed as being too close to the interior ministry and other government institutions, and having failed to keep families and victims adequately informed of progress in their investigations.

In the most widely known case, Nabeel Rajab is facing up to 15 years in prison for free speech offences that include writing an article critical of the government in the New York Times.

Amnesty International UK’s head of policy and government affairs, Allan Hogarth, said: “It was a welcome move when Bahrain set up these two bodies back in 2012, but it’s utterly disingenuous of the UK government to pretend they’re delivering substantial human rights reform in Bahrain.

“Instead of acting as overexcited cheerleaders for Bahrain’s woefully inadequate reforms, UK ministers ought to be confronting the awkward reality that these UK-backed institutions are seriously flawed and widely seen as a PR tool of the Bahraini government.”

Amnesty said authorities have placed severe restrictions on the right of Bahrainis to participate in demonstrations and other forms of peaceful assembly. There is an indefinite ban on all public demonstrations in the capital.

The security forces regularly disperse unauthorised protests, which mostly occur in Shia villages when protesters demand the release of political prisoners, sometimes using excessive force including teargas and shotgun pellets, it said.