LONDON (Reuters) -Britain and the United States have agreed a technology pact to boost ties in AI, quantum computing and civil nuclear energy, with top U.S. firms led by Microsoft pledging 31 billion pounds ($42 billion) in UK investments.

The "Tech Prosperity Deal" is part of U.S. President Donald Trump's second state visit to Britain, which will include a day of pomp at Windsor Castle on Wednesday, hosted by King Charles and the royal family.

Britain said the pact included joint efforts to develop AI models for healthcare, expand quantum computing capabilities and streamline civil nuclear projects. It added that it would support economic growth, scientific research and energy security in both countries.

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British Prime Minister Keir Starmer said the deal had the potential to shape the future of millions of people on both sides of the Atlantic, and deliver growth and security.

The U.S. is Britain's single largest country trading partner, and its big tech companies have already invested billions of dollars in their UK operations.

Starmer, under pressure to reverse years of weak economic growth, now wants to pitch Britain as a destination for further investment by opting for the light touch regulation favoured by the United States in areas such as AI, as opposed to the more interventionist approach of the European Union.

The Trump administration has criticised European online safety laws and digital taxes, including those in Britain, but they were not part of the discussions over the pact.

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Under the deals announced, chipmaker Nvidia said it would deploy 120,000 graphics processing units across Britain - its largest rollout in Europe to date.

It is working to deploy up to 60,000 Grace Blackwell Ultra chips with UK-based Nscale, which will partner OpenAI in a UK leg of the U.S. company's giant Stargate project and tie-up with Microsoft to establish Britain's largest AI supercomputer.

Microsoft said it would invest 22 billion pounds in total to expand cloud and AI infrastructure as well as in the supercomputer, which will be in Loughton, north-east London.

Satya Nadella, chair and CEO of Microsoft, said it wanted to ensure that America remained a trusted and reliable tech partner for Britain. Its president, Brad Smith, said relations had improved hugely since the "dark days" before the UK's antitrust regulator dropped its opposition to Microsoft's acquisition of Activision Blizzard, saying he felt "enormously better".

David Hogan, vice president for enterprise at Nvidia, told reporters the investments would "truly make the UK an AI maker, not an AI taker".

  Google announced a 5 billion-pound investment, including a new data centre in Waltham Cross, north of London, and continued support for AI research through its DeepMind project.

Cloud computing firm CoreWeave said its 1.5 billion pound backing would fund energy-efficient data centres in partnership with Scottish firm DataVita, bringing its total UK investment to 2.5 billion pounds.

Other firms announcing commitments include Salesforce, Scale AI, BlackRock, Oracle, Amazon Web Services and AI Pathfinder, with investments ranging from hundreds of millions to several billion pounds.

($1 = 0.7336 pounds)