Question to the Ministry of Defence:

To ask the Secretary of State for Defence, whether any components of the (a) Mk4 and (b) Mk4A Holbrock warhead were (i) manufactured in and (ii) procured from the US, other than the (A) arming, (B) fusing and firing system, (C) neutron initiators and (D) gas transfer system.

In addition to the Mk4/4a components listed by the hon. Member, the UK acquires the Mk4 aeroshell from the US under the auspices of the 1963 Polaris Sales Agreement (as amended in 1982 for Trident). Utilising US non-nuclear warhead components brings significant cost benefits and ensures we remain compatible with the Trident missile, however, the requirements, design and manufacture of the Holbrook warhead are independent to the UK.