Question to the Ministry of Defence:

To ask the Secretary of State for Defence, what the in-service date is for the UK Trident Mark 4A modified warhead; what the estimated cost of the Mark 4A programme is; and what progress has been made in delivering that programme.

I am withholding details of the date of the Mk4A component's entry into service, the cost of the Mk4A programme and the progress made to date in delivering the programme for the purposes of safeguarding national security.

The Top Level Budget for the Mk4A programme is held by Director General Nuclear.