This announcement comes after the UK government previously said it “would not hesitate to act” to protect one of its largest companies from a foreign takeover.
BT shares plummeted last year following the announcement that the billionaire owner of Altice Patrick Drahi had increased his stake in the company from 12% to 18%.
Shares fell a further 4% after the review was announced.
The assessment of the deal by business secretary Kwasi Kwarteng has 30 days to come to a conclusion – which could be extended to 45 if necessary and that process is now underway.
A statement released on the gov.uk website added: “The government has powers under the National Security and Investment Act 2021 to scrutinise and – if necessary – intervene in qualifying acquisitions on national security grounds.”
The UK previously welcomed investment but a full takeover of its plans could hinder its £15 billion fibre transformation programme.
Drahi has previously insisted he does not intend to launch a full takeover of the company, however, June will see the takeover code that prevents a new bid, expire.
In a statement, BT said it “will fully cooperate with the review”.