Thank you Boffin, Doing a bit of digging I found this "https://researchbriefings.files.parliament.uk/documents/CBP-8166/CBP-8166.pdf". Well worth a read. If I have read the 1st para under Acquisition costs (page 10) correctly the original capitol cost of Trident came from central funds with defence picking up the running costs. As for the Trident replacement "Para 4.4 Who will pay for it" page 19 is an interesting read.