I know how we can save the defence budget... by making cuts elsewhere.
Sell of the Houses of Parliament. Would make a lovely hotel. Build a new parliament on the outskirts of Birmingham, but don't fund it properly so they have to share rooms. Would save a fortune in housing costs for MPs. Then slash MPs pensions. Also scrape their allowances to buy property, and say, give them a loan of £8,5000 instead.
Only pay enough travel to go home every couple of weekends. Give cabinet ministers old landrovers and say that they will be safe from terrorists. Mmmm.
Or... instead of moving them to Birmingham, put them up in an old MOD base. Let them share accommodation, and keep saying, "We were going to build all new blocks, but the government has only funded enough for half of you."