Downing Street is to raise the number of Trident nuclear warheads the UK can stockpile by more than 40 per cent in its integrated review of defence, security and foreign policy to be published on Tuesday.

Boris Johnson, UK prime minister, is set to announce that the cap on the number of nuclear warheads will increase from its current level of 180 to 260, according to two people with knowledge of the document. The move — which signals a move away from Britain’s pursuit of non-proliferation in recent decades — is intended to cement the UK’s status as a nuclear power and firm US defence ally.

The 100-page defence and diplomatic strategy, “Global Britain in a Competitive Age”, promises to be the most comprehensive review of UK foreign policy since the cold war and will allow the prime minister to describe his post-Brexit vision for the country. However, it has been repeatedly delayed while ministers focused on the coronavirus pandemic.