The announcement was made on the first day of a Qatar-UK business investment forum hosted by International Trade Secretary Liam Fox and comes in the week when Mrs May will formally start the process of leaving the European Union.
"I am still looking, even after Brexit there will be opportunities QIA can really hunt for", QIA Chief Executive Sheikh Abdullah bin Mohammed bin Saud al-Thani told the conference.
Earlier, the head of the country's sovereign wealth fund said he still saw opportunities to invest in Britain after it quits the bloc.
Qatar's sovereign wealth fund plans to expand in the United Kingdom and the US, as top officials said long-term commercial opportunities would outweigh political uncertainty roiling the two countries.
Qatar already has more than £40 billion invested in the United Kingdom, including ownership of London's tallest building The Shard, Harrods department store and the Olympic Village.
Qatar, the world's biggest exporter of liquefied natural gas, is already a major investor on both sides of the Atlantic.
Theresa May hopes to deepen ties with Qatar after the oil-rich Gulf state announced it will invest £5 billion in the United Kingdom over the next few years. "Certainly we can contribute to the UK's need", said Sada.
Qatar, too, has a big stake in keeping the United Kingdom economy and asset prices strong during and after Brexit.
Qatari investors put billions into Barclays bank during the 2008 financial crisis and have created a stock and property portfolio worth over $50.27 billion (40 billion pounds) over the last decade.
Yet the Qatari royal said the wealth fund still agreed to commit "a big amount of investment in the United Kingdom, especially in infrastructure" during its last strategy session. Information technology is among the top priorities for the fund, officially known as the Qatar Investment Authority, along with healthcare and infrastructure, Al Thani said, aiming to turn Qatar into a knowledge-based economy. Officials are seeking more investment flows as the country diversifies its economy away from oil and gas and continues a $200 billion infrastructure upgrade before the 2022 World Cup.
Al Emadi said Qatar's investments in the USA are "really ahead of schedule".
The new office follows several acquisition deals, among them the largest poultry producer in Turkey, Russia's Rosneft, and British utility National Grid.