The United Kingdom scientists have welcomed a surprise government promise to invest an extra £2 billion (US$2.5 billion) per year into research and development (R&D) by 2020 - although details of the pledge will not be made clear for at least another two days.

In a speech delivered in London on 21 November, Prime Minister Theresa May declared that her government would "commit to substantial real terms increases in government investment in R&D - investing an extra £2 billion a year by the end of this Parliament to help put post-Brexit Britain at the cutting edge of science and tech".

May said that some of the investment would be made through a new Industrial Strategy Challenge Fund - which, she added in an article for the Financial Times, would be used to back R&D in technologies such as robotics, artificial intelligence and industrial biotechnology.

"I'm impressed. The Prime Minister's commitment to make our strength in science and innovation the cornerstone of the UK's future couldn't be clearer," said Sarah Main, the director of the London-based Campaign for Science and Engineering.

A government statement noted that the promised investment would be "worth £2 billion per year by 2020", a wording that implies that it could be made in the form of subsidies other than direct funding, such as tweaks to the tax credits that companies are offered for performing research-related activities. Some researchers, including James Wilsdon, who studies research policy at the University of Sheffield, immediately questioned how much of the investment would take that form.

The government says that it currently invests around £6.3 billion directly in R&D (not including separate funding for higher-education institutions) and more than £2 billion in R&D tax credits. But details about the new investment are scarce: government press officers said they could not provide details until after an annual statement on government spending, to be delivered on 23 November.