International defence analysis firm IHS Jane's says that Britain's military budget is set to be outstripped by its former colony by 2017, as the country drops to sixth place from fourth in terms of global military spending.
The UK will fall behind Russia this year and slip further and come neck-and-neck with India by 2016.
"The reality is that our armed forces' ability to prosecute core tasks is being diminished. Our capability does not meet requirements," senior analyst Ben Moores said.
The UK, by comparison, spent USD 58.6 billion in 2013 and is projected to shell out USD 59.6 billion in 2020.
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The US will remain in the lead, spending USD 637.8 billion this year and a projected USD 538.2 billion in 2020.
Britain's Ministry of Defence (MoD) disputes some of the figures and describes the predictions as "speculation".
But the Stockholm International Peace Research Institute says that given UK budget forecasts and India's projected economic growth the figures are reasonable.
It was a record low for India, with the figure dropping considerably from 3.16 per cent of GDP in 1987 to 1.79 per cent.