The Government will allow those who tried but failed to boost their state pension last week – before top-up prices rocketed by 50% today – more time to pay the reduced rates.

The extension, granted by the Department for Work and Pensions (DWP), comes after its official online state pension forecasting system crashed last week due to huge demand. This left thousands unable to work out whether paying extra now, could boost their retirement income.

However, you must contact the Pension Service as soon as possible, or risk paying the hugely inflated cost, if you couldn't get a forecast in time.

The price of buying an extra year’s NI in most cases soared from £421 a year to £626 a year today, the start of the 2009/10 tax year. However, the DWP said last Friday that if you requested a pension forecast by the end of the weekend just gone, but receive the forecast afterwards, you can pay at 2008/09 rates if done within a month of receiving the forecast.

But we have learned today that if you if you couldn't access the online forecasting system before the end of the past tax year, or the phones were jammed, the Government's Pension Service may extend the deadline for you, if its records show there were problems when you tried.

It's likely you'll get another month from the moment you eventually get a forecast. But you'll need to call the Pension Service as soon as possible on 0800 731 7898 as this concession could be withdrawn at any time.

To get the full Basic State Pension, you need to have paid National Insurance (or received qualifying benefits) for 30 years if you reach state pension age after 5 April 2010. If you've reached, or will reach, pension age before then, men need to have paid NI for 44 years and women for 39 years.

However, many people can buy Class 3 NI contributions to make up any shortfall. Our State Pension Boosting calculator will help you work out how long you need to live to make your money back if you buy extra NI.

A DWP spokesman says: "We are very sorry that some customers have been experiencing difficulties with our pension forecasting service over the past few days.

"Due to unprecedented demand for our usually reliable service, some people have experienced delays in applying for a pension forecast. We are doing everything possible to prevent further problems from occurring."

Today, the Basic State Pension entitlement rose from £90.70 a week to £95.25 a week.