Commonwealth countries will be given help by the UK to meet international standards as Theresa May set out plans to boost trade within the organisation.

Brexiteers have championed the idea of boosting trade links with the Commonwealth after leaving the European Union and the Prime Minister’s move sought to make it easier for businesses to operate more freely within the 53-nation group.

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But as leaders gathered in London for the Commonwealth Heads of Government Meeting (Chogm), Mrs May did not address a mounting controversy over the status of Windrush generation immigrants in the UK.

Prince Harry and Theresa May at the Commonwealth Youth Forum (Simon Dawson/PA)Prime Minister Theresa May and Prince Harry at the Commonwealth Youth Forum (Simon Dawson/PA)

In a speech at the Guildhall in the City of London, the Prime Minister called for the Commonwealth to become a beacon of free trade at a time of fragile international growth and continued protectionism.

Trade within the Commonwealth is valued at £393 billion and estimated to rise to £492 billion by 2020, according to the Government.

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Mrs May promised British help for developing countries to meet existing standards for their products.

“Shared standards have huge potential to stimulate trade,” she said.

“They create a common language for trading partners across the globe, enhance trust in supply chains and stimulate innovation.

“Greater use of these international standards across the Commonwealth will reduce the costs of trade between members, as well as with partners beyond the Commonwealth, for greater global benefit.

“That is why the UK will be funding an all-new Commonwealth Standards Network, which will support developing countries in particular to better meet existing international standards.”

The Prime Minister also announced that the UK will support a programme of technical assistance to Commonwealth countries to implement the terms of the World Trade Organisation agreement on trade facilitation.

Full implementation is estimated to reduce trade costs by as much as 16% for less-developed countries, while cutting the average time needed for goods imports by 47% and exports by up to 91%, she said.

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But she warned: “No amount of action on these fronts will truly be successful if half the Commonwealth citizens continue to face significant barriers to participation in the economy.

“If our family of nations is to realise its full potential, then we must take action to boost women’s access to economic opportunity and empower them to create and to build their own businesses.”

Announcing plans for the UK to work with the International Trade Centre on a new She Trades Commonwealth initiative to break down gender barriers, Mrs May said: “Boosting women’s participation is the right thing to do, but business equality is not just about doing what is right, there are real economic benefits.”

She cited estimates that global GDP could be increased by up to 28 trillion US dollars (£20 trillion) if women played the same role as men in the labour market.

Ahead of her speech, Mrs May attended a Commonwealth Youth Forum event with Prince Harry.

Chogm gathers every two years to discuss shared interests and challenges.

As this year’s summit began, the PM was under pressure to address the concerns of long-term British residents from the so-called Windrush generation over their immigration status.

The move follows concern that people are facing deportation and being denied access to healthcare due to UK paperwork issues and anomalies affecting some immigrants who arrived from Commonwealth countries between the late 1940s and early 1970s.

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Meanwhile, Labour called for Mrs May to use the summit to apologise for past failures by the British Government.

Shadow foreign secretary Emily Thornberry said Margaret Thatcher had ignored efforts by every other Commonwealth member to bring apartheid to an end in South Africa in the 1980s.

She also urged Mrs May to support other Commonwealth members in their efforts to right the “historic wrong” of the Chagos Islands.

The Indian Ocean territory has been a contentious issue for years, with most of the island’s 1,500 inhabitants deported so that the largest island, Diego Garcia, could be leased to the US for a strategic air base in 1971.