This seems new: https://www.gov.uk/government/publi...idia-corporation-public-interest-intervention
Proposed acquisition of ARM Limited by NVIDIA Corporation: public interest intervention
Under the powers set out in the Enterprise Act 2002, the Secretary of State for Digital, Culture, Media and Sport is able to intervene on national security grounds. This responsibility is discharged in a quasi-judicial capacity.
On 19 April 2021, the Secretary of State issued a public interest intervention notice (PIIN), confirming that he is intervening in the sale on national security grounds. In reaching this decision, he considered advice received from officials across the investment security community.