The MOD spends around 1.8% of GDP on defence capability (Picture: MOD).
The Defence Select Committee has published a report which reveals the decline in defence spending.
Government expenditure totals are measured as a proportion of the nation’s economy - known as Gross Domestic Product (GDP).
The new report claims the Ministry of Defence (MOD)'s expenditure as a percentage of GDP has decreased by a larger proportion than that of other departments, such as Health and Education.
The MOD spends around 1.8% of GDP on defence capability - with next year's budget sitting at around £37.6bn.
The figure is well below that of other departments such as Education (4.2%), Health (7.1%) and Pensions and Benefits (11.1%).
The Defence Select Committee says the numbers look even smaller if you wind back the decades.
"When you compare what we used to spend in the 1980s on defence, health and education, it was 4.5 to 5.0% of GDP on each," said the Chair of the Defence Select Committee, Julian Lewis.
"Now, we spend two and a half times on education and four times on health of what we spend on defence," he added.
The report comes as MPs debated Defence spending in Westminster Hall.
"Defence is an insurance policy," said Anne-Marie Trevelyan MP, from the Public Accounts Committee.
"If we get our deterrent right, it stops wars and attacks on us or our allies."
"That is a success, but it is invisible," she added.
Despite the numbers, the UK is still one of a small number of countries that meets the NATO target of spending 2% of GDP on Defence.
The NATO calculation adds other expenditure such as peacekeeping and pensions to the Defence budget – the UK currently hits 2.1% under the NATO calculation.
The Ministry of Defence says: "Under the official NATO calculation, the UK continues to spend more than the required 2% GDP on defence," said the MOD.
"The NATO figure is an important measure because it is consistently applied across the alliance to ensure members meet their commitments," a spokesperson added.
"The UK is one of only a small number of countries to meet the NATO target to spend 2% of GDP on defence.
"We have the largest military budget in Europe and are the second largest spender in NATO, behind only the United States."