Liverpool, ENGLAND — U.K. finance chiefs are banging the drum for pension reforms to boost anaemic investment and growth in the country.

The annual Labour conference — the centre-left party's first in power for 15 years — was awash with delegates from the City of London urging the government to move decisively with plans to make retirement schemes more competitive.

William Vereker, chairman of Santander U.K., cited pension reform as one of three paths to economic growth, alongside skills and education, and regulation.

"We are almost wholly reliant for investment in this country at the moment, on the kindness of strangers. We're reliant on external companies, external investors and so on, to invest in our stock markets, invest in our businesses, and that just isn't sustainable," Vereker told a room full of industry figures on Monday.

"If we do not have domestic capital investing in domestic businesses, we will not see the growth that this government is so rightly focused on," he added.

BlackRock's vice president of government affairs and public policy, Muirinn O'Neill, said the new government had a "once-in-a-generation" chance to overhaul the pensions system.

"In terms of the growth agenda, we have been long-term champions of getting more DC investment into private markets," she said Tuesday, referring to defined contributions, which are retirement plans based on money paid in as opposed to money earned.

The comments echo those from Citi U.K. CEO Tiina Lee, who told CNBC last week that domestic funds have for too long focused on low-risk and low fee investments, leading to "sub-optimal" returns.

"For me, pension reform is the way to unlock growth in the U.K.," Lee told "Squawk Box Europe."

"When one thinks about the amount of long-term capital there is here in the U.K., it's nearly £5 trillion held in pension funds and insurance companies. In order to actually unlock even a fraction of that, to put into long-term infrastructure projects that ultimately will drive growth is absolutely the right route," she said.

U.K. Finance Minister Rachel Reeves in July announced a landmark pensions review as part of a "big bang" of reforms to unlock growth. The measures include plans to consolidate local government pension schemes into a larger fund, and increase allocation to U.K. high-growth businesses.

Such investments could serve to further the U.K.'s strategic interests, for example by bolstering regional development, vital infrastructure, medical innovation and decarbonization, according to the government.

Economic secretary to the Treasury, Tulip Siddiq, said Monday that raising the risk appetite of pension funds to invest more heavily in equities was critical to Labour's wider national renewals plans.

"If we don't unlock the capital in pension funds, we're not getting anywhere — and that's about putting investment into our country," she said.

U.K. pension schemes have some of the lowest share of funds held in domestic stocks and private assets of any major global pension market, according to think tank New Financial. Just 4.4% of U.K. pension assets are currently held in domestic stocks, down from an estimate of 6.1% last year and well below the global average of 10.1%.

Reeves has said that the U.K. could model itself on Canada, where megafunds invest in stocks and infrastructure. According to the New Financial, the so-called Maple 8 group of retirement funds have around 3% of assets in domestic listed stocks but a further 22% in private equity and 12% in infrastructure.

"The size of Canadian pension schemes means they can invest far more in productive assets like vital infrastructure than ours do," Reeves said last month.

The U.K.'s local government pension scheme, which manages £360 billion worth of assets for 6.6 million public sector workers, is currently fragmented into 86 individual funds in England and Wales. If it were combined into a single fund, it would rank as the seventh largest in the world.

A flagship International Investment Summit next month will be a key test of the government's ambitions to catalyse further investment, with around 300 industry executives expected to attend.

Boosting both domestic investment and increasing returns will be a difficult needle to thread, however. Nathan Long, senior policy analyst at financial services firm Hargreaves Lansdown, said policymakers need to be clear-eyed about the reforms' objectives and the time that will take to flesh out.

"What happens if those returns don't come through for five, 10 years because of the type of asset class that you hold?" Long said at the conference Tuesday. "All of a sudden your scheme looks like it's underperforming when actually it's not at all, it's a by-product of where you've decided to invest for the longer term."

BlackRock's O'Neill, meanwhile, urged "joined up thinking" from the government to simultaneously try to tackle the country's chronic lack of savings alongside pensions reform.