At present, published government policy is strongly to discourage the deployment of private armed guards on board UK flag vessels, but HMG are now considering amending this to a position which recognises that engaging armed personnel is an option for UK flagged ship owners to combat piracy in exceptional circumstances.
The Home Office is currently looking at the applicability of UK firearms legislation on board UK flag ships on the high seas. If legal opinion is that the Firearms Act 1968 does apply, a decision will need to be made as to whether it is appropriate and feasible to grant the authority of the Secretary of State for the possession of prohibited firearms (classes of firearms that are not sanctioned to be kept on board as part of ships equipment) in these circumstances. On the assumption that the Firearms Act 1968 does apply to UK flagged ships on the high seas, without such an authority it would be illegal to carry such firearms on board UK flagged ships. Even in circumstances where possession of firearms is duly authorised, their use must also be lawful. Use of such weapons other than in self defence or defence of others risks criminal (and civil) liability.