To ask the Secretary of State for Defence what assessment he has made of the likely effect of the introduction of the Mk4A Arming, Fusing and Firing system on the (a) ability to accurately adjust the height of burst of the Trident warhead and (b) probability that the Trident warhead will be effective against hardened targets. (129539)

The MK4A Arming, Fusing and Firing system is a non-nuclear component being introduced into the UK Trident warhead to replace a similar component which is becoming obsolete. This is necessary to ensure that we can keep the existing warhead in service in the 2020s. I am not prepared to discuss the detailed performance characteristics of our nuclear weapons.