M&G's Richard Woolnough said the possibility of another £375bn in asset purchases by the Bank of England means gilt yields could remain at record lows for years to come.
The Bank last week announced a £50bn expansion of its quantitative easing programme, bringing the total to £375bn and leading to fresh questions of how far the Bank will go with its asset purchases.
Woolnough said comments made last month by governor Mervyn King, indicating the UK is not yet halfway through its economic crisis, suggest another £325bn of QE may yet materialise.
"The BoE base rate has been set at 0.5% since March 2009, and over £325bn has been pumped into the financial system through QE," said the manager of the £8.1bn Optimal Income, £6.2bn Corporate Bond and £5bn Strategic Corporate Bond funds at M&G.
"If we are not yet halfway through this crisis, then this implies that rates will stay at these levels for at least another three years to 2015, and a further round of £375bn of QE is potentially on the agenda."
This outlook makes ultra-low gilt yields look more logical, Woolnough added, and the likelihood of a concurrent global recovery means record low bund and treasury yields "may also make sense".
Last month Schroders' Strategic Bond fund manager Gareth Isaac said the Bank would continue buying gilts until it owned all of the market not held by life companies - equivalent to roughly £600bn in assets.
Economists at Citigroup, meanwhile, expect QE to be expanded "a lot further", reaching around £500bn in total.
"This is likely to come alongside liquidity easing, credit easing and - if the EMU crisis remains severe or escalates - emergency tax cuts to slow the planned fiscal tightening for 2013".
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