Asked why the funding was set to come out of the MoD's budget - when the yacht will be classified as a trade ship rather than a military vessel - the spokesman replied that Defence Secretary Ben Wallace had responsibility for UK shipbuilding. He added that Mr Johnson wanted the yacht to be built in the UK but would ensure the process was compliant with all international rules on procurement.
If it officially has a defence role and ordered by the MOD then the government can insist it is built in the UK.
If it was being ordered any other way then, under the trade deal signed with the EU, it would have to go out to open tender Europe wide.