Employees working in medium-sized and smaller companies are starting to have pension contributions automatically deducted from their pay by their employers.

This is part of auto enrolment, the government's scheme to get more people saving for retirement.

While the first phase of auto enrolment involving larger firms appears to have been successful, prompting the government to halve its estimate of the numbers who will opt out of the scheme, there is also growing scepticism about whether that will continue.

A survey by Legal & General earlier this month claimed that six out of 10 small businesses in Scotland due to start enter the auto enrolment process this month could fail to meet their obligations. Low earners, meanwhile, are in danger of falling through the net.

The attraction of auto enrolment for employees is that their employer must also contribute to their pension. To start with, each must contribute a modest 1% of gross earnings. But minimum contributions will gradually rise and by late 2018, the total will have reached 8% - at least 3% from the company, up to 4% from the employee and 1% tax relief.

The scheme will continue in Scotland whatever the result of the referendum.

Ian Naismith, senior pensions manager at Scottish Widows, says: "The Scottish Government has pledged to continue with auto enrolment in the event of independence."

So far only the largest companies have had to auto enrol their staff. Now medium-sized companies must follow suit. This month employers with 249 to 160 staff have had to start the process, and from May, those with between 159 and 90 employees must do so. Smaller companies will gradually be drawn into the net. From June 2015, it will affect companies with less than 50 employees and by the end of the process in 2017, every employer will be covered.

Employees do not have to agree to auto enrolment.

Pensions expert Steve Bee, of Jargonfree Benefits, explains: "Employees can opt out at any time but they will only get their contributions back if they opt out within six weeks.

"After that, they can stop their contributions but previous contributions will stay invested in the pension until they reach retirement age."

The UK government recently gave itself a pat on the back because fewer people have opted out so far than originally expected. Among the largest employers opt-outs have been running at just 10%. This has led the DWP to halve its forecast of total opt outs from 30% to just 15%. It has increased its projection of new pension savers as a result of auto enrolment from 8 million to 9 million.

However, Laith Khalaf, head of corporate research at Hargreaves Lansdown, believes the government has got ahead of itself. He says: "Early signs from the auto enrolment programme are encouraging, but much of the heavy lifting still needs to be done."

Experts put the early success down to the fact that large companies have been well equipped to communicate the benefits of pensions to their staff, while pension providers have found it commercially attractive to help them.

But David Trenner, technical director of Intelligent Pensions in Glasgow, which works with employers, thinks the situation will now change. He says: "Very few medium and smaller employers are well-prepared to deal with pensions."

Mr Trenner believes smaller employers will be reluctant to pay extra for an auto enrolment communications exercise after they have had to meet the cost of setting up the pension scheme and budgeting for contributions, as it is not in their interests. Although they can't tell their employees to opt-out, it would save them money if this happened.

Mr Bee is more optimistic. He says: "In my experience employers want to comply with the legislation and are being more generous and adding more benefits than they need to. Among employees one of the interesting things we have found is that, contrary to expectations, young people are no more likely to opt out of the scheme than others. If anything their attitude to saving is stronger."

However, it was Mr Bee who suggested after the Budget that "pensions should be put out to pasture". He explains: "All I meant is that I don't think people should have to decide at the point of saving whether the savings are going to be for the short, medium or long-term.

"Helping people make that type of decision is advice intensive. If they just want to save money, they should be able to access a tax-efficient savings vehicle and decide what they want to do with the money later."

This more flexible type of arrangement would probably be more useful for lower earners - precisely those who are excluded from being auto-enrolled because their earnings are too low. Tom McPhail, head of pensions research at Hargreaves Lansdown, says: "Around 2.9m people have been auto-enrolled, but even more - 3.6m - have not, and one of the main reasons is because they earn below the minimum earnings limit, currently £10,000. One of the challenges for the Government will be to sweep up those people who are falling through the cracks in the system."