The Adam Smith Institute says the move to raise the state pension age to 68 earlier than planned fails to go far enough.

The Government announced this week that the increase from 67 years old will now be phased in between 2037 and 2039. It had been scheduled to happen from 2044 in the first plans.

Six million men and women will have to wait a year longer than they expected to get their state pension, it has been estimated.

Those who will affected are currently aged 39 to 47.

The Adam Smith Institute, a leading think tank, said it welcomed the Government's move but called on it to “go further, faster”.

Ben Southwood, head of research at the institute, said: "The Government has seen sense by raising the retirement age, but they should up the pace.

"Retirement should be more of a steady decline in work than an abrupt cliff. Today our sub-replacement fertility, combined with our steadily improving healthcare, mean that a smaller and smaller working population support a larger and larger group of dependent elderly.

"The mandatory retirement age, combined with the new flat rate, which reduces the disincentive to building up wealth, are steps in that direction. Retirement age hikes are another.

"The evidence from retirement age reforms is absolutely clear: they have huge effects on labour hours for older workers. Not only do later retirement ages mean that older workers take out less—they also pay in more.

"Politicians, and society in general, are usually far too relaxed about the upcoming population bomb, but this move, at least, makes the situation a bit less difficult."