As part of Theresa May’s £1 billion deal to buy the support of the DUP so she can stay in power, defence spending will be at least maintained until the next general election.
So there’s not much point campaigning for any kind of reduction for the next four or five years.
Specifically: “On defence, the parties have said they will ensure they meet the NATO commitment of spending two per cent of GDP on the armed forces, as well as committing to the Armed Forces Covenant. They will also look at ways to support reserve forces in Northern Ireland.” UK GDP is just over £2,000,000 million, 2% of that is about £40,000,000,000 or about £750,000,000 per week.
Note that it is 2% of the Gross Domestic Product which is the entire output of the economy, not 2% of the tax income, nor 2% of government expenditure.