By Adam Uren

PUBLISHED: 08:58 EST, 19 August 2013 | UPDATED: 09:11 EST, 19 August 2013

Almost a fifth of over-65s still in work do not know when they will be able to stop because they haven't set enough aside to retire on, research from Barings Asset Management claims.

One in five surveyed said they haven't set a definite date to retire, though most think they will probably keep on working until they're at least 71.

Adding to the growing fears about the financial security in retirement of millions of Britain's future pensioners, a third of those approaching retirement, aged 55 to 64, said they also don't know when they will be able to retire.

Marino Valensise from Barings, said: 'It is clear that uncertainty is increasing for many people around retirement plans, with more people unable to say exactly when they plan to retire and the average age continuing to rise.

'Significant numbers of people nearing traditional retirement age reported they did not know when they will be able to retire and the worry is that a lack of sufficient financial planning and pension provision, combined with increased longevity, is having a real impact on a large proportion of the population.'

The Government is attempting to head off a future pensions crisis through automatic enrolment, which sees pensionless workers placed onto savings schemes.

But in spite of this, there are millions of workers who are approaching retirement with little or no pension savings, and many of those who do have them have no saved enough to adequately replace their working wage.

Just over a third of people told Barings they didn't have a pension, a figure Barings described as 'alarming'.

Mr Valensis said: 'The fact that so many people say they do not have a pension, including relatively affluent people and those in the 55-64 age segment, underscores the need to focus on effective retirement planning.

'We are alarmed that so many people who should have proper plans in place do not, and urge everyone to better understand the benefits that they can get from planning ahead and starting early.'

In future decades adults will be required to work for longer anyway, with the state pension age rising to 66 for men and women in 2020, 67 in 2028 and 68 at some point in the 2040s.

By the time the UK's youngest workers come to retire, it is likely that they will be working beyond the age of 70 before they can get their state pension.

The reality that people will be retiring later is starting to sink in among respondents to Barings' survey, with people saying on average they expect to retire at 64, which is up from the average of 62 following a similar survey in 2009.