The first British ministerial visit to Hong Kong since the introduction of draconian Chinese security laws five years ago was a chance to demand that China unlock more than £2bn in pensions belonging to British overseas passport holders who fled for the UK, former cabinet ministers have told the Foreign Office.

A letter signed by more than 90 MPs, including 10 former ministers, urges the trade minister Dominic Johnson to do more to release frozen savings belonging to thousands of Hongkongers.

Lord Johnson’s three-day visit to Hong Kong heavily focused on attracting investment into the UK, in the latest sign of a carefully managed thaw in relations between the UK and China.

The pension freeze, one of many roadblocks to restored relations, came as a consequence of the Chinese foreign ministry saying it would no longer recognise the British national (overseas) passport as an identity document in January 2021.

In a cross-party letter signed by senior Tories including Chris Patten, Malcolm Rifkind, Iain Duncan Smith and David Davis, Johnson was told that “the punitive denial of Hongkongers to access their savings is curtailing the ability of many to start new lives and to prosper and thrive in the UK”.

The money is held in a mandatory provident fund whose trustees include HSBC Bank. The letter presses the trustees, including HSBC, to ensure Hongkongers regain access to their savings.

The letter states: “In the case of HSBC, a UK-headquartered bank is undertaking retaliatory action on behalf of the Chinese government and it is estimated that it has denied access to over £600m hard-earned savings.”

The letter proposes that the UK government challenges Beijing by issuing unilateral guidance to all UK-based financial institutions regarding the use of BNO passports as valid documents.

In a Commons written reply on 4 May, Anne-Marie Trevelyan the minister for the Indo-Pacific, did not suggest any unilateral step. She said: “We are aware of the difficulties British national (overseas) passport holders are experiencing in seeking early withdrawal of their pension held by the mandatory provident fund in Hong Kong … We have urged the Hong Kong authorities to facilitate the early withdrawal of funds, as is the case for other Hong Kong residents who move overseas permanently. I raised this issue with Christopher Hui, Hong Kong secretary for financial services and the treasury, on 18 April and pressed for a pragmatic solution.”

In a further sign that Hong Kong is being swallowed into the jurisdiction of mainland China, its legislative council passed a controversial bill on Wednesday that allows Hong Kong authorities to ban overseas lawyers from taking part in local cases involving national security.

The two-stage vetting system under the new amendment was proposed after the Hong Kong government’s failed legal battle to ban the jailed media tycoon Jimmy Lai from hiring a British barrister, Timothy Owen, to represent him at his trial for alleged collusion with foreign forces.

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