Millions of retirees face being targeted by fraudsters trying to get their hands on their pension pots, the pensions regulator has warned.

From next month, over-55s will be able to access their full retirement funds in a lump sum for the very first time. Until now, most workers have only been able to exchange their savings for a small income every month through an annuity.

But with millions of retirees gaining access to pots of cash worth sometimes hundreds of thousands of pounds, the fraudsters are already circling, looking for opportunities to fleece them.

Warning: Retirees could be bombarded by cold callers looking to get their hands on their pension pots

Pensioners could be bombarded by cold calls and texts promising a 'free pension review' or mentioning a 'legal loophole' to access their cash.

Pensions Minister Steve Webb said: 'You can spend years saving into a pension only to find yourself tricked out of your money in the blink of an eye by these unscrupulous crooks.

Crooks targeting over-55s could become a plague' on daily life bombarding people using similar tactics to PPI claims companies, he told the Daily Telegraph.

The pensions regulator is launching its 'scorpion' campaign today to alert retirement savers to the risks. It warns that scammers will try to flatter, tempt and pressure victims into transferring their pension fund into an investment with attractive and often unrealistic returns.

Once the victim has signed the forms and the transfer has gone through, they are unlikely to see their money again and could be left with a hefty tax bill.

The warning comes ahead of major pension reforms, which will take effect from April 5. Under these changes, savers will no longer have to convert their pension savings into an annuity, which takes the money pension savers have built up and pays a guaranteed income for life in return.

Instead they can take the full sum at once – although they will have to pay tax on whatever they withdraw at income tax rates – or they could invest it and take an income more gradually.

Millions more pensioners who have already bought an annuity will be able to cash it in under further reforms set to be announced by chancellor George Osborne in the Budget this week.

Five million retirees are locked into one of these retirement deals, which mean that their savings are locked away but in return they are guaranteed an income for as long as they live.

The radical plan would mean these pensioners could sell their annuities for a cash lump sum.

George Osborne explained that pensioners should have the freedom to manage their retirement incomes. He added that it was 'patronising' to suggest that OAPs would make poor decisions, such as using their retirement funds to fund expensive holidays or fast cars.

He said yesterday: 'I just think that is a very patronising attitude to take towards people who have shown responsibility, saved through their lives, saved for a pension. By changing the law we are trusting people who have worked hard and saved hard all their lives.'

Warning: Pensions minister Steve Webb said retirees should watch out for scammers offering bogus investment schemes

However Labour and consumer groups have warned that this too could spark a new misselling scandal as pensioners who are allowed to do what they like with their cash make the wrong decisions.

Joanne Segars, of the National Association of Pension Funds, expressed concerns, saying: 'It's clear to see how this fits with this Government's agenda for pensions but what is less clear is how savers will be protected.'

Steven Cameron, of life insurance firm Aegon, added: 'Anyone turning future annuity income into cash is giving up a guaranteed flow of income – for their and possibly a partner's future life. Swapping this for a lump sum, calculated based on a range of factors, is undoubtedly a complex and risky decision and specialist advice would be essential.'

The selling of annuities has been mired in scandal over poor selling techniques, which has meant many may have missed out on the best deals.

Some people who are in bad health complain their insurer did not tell them they were entitled to higher monthly payments because of their lower life expectancy.

Married couples were not advised to take joint-life annuities, meaning the surviving spouse was left with no income after one died and the payments stopped.

Retirees also do not always realise they can shop around for an annuity and so are tied into one from their pension provider, which may be a considerably worse deal than others available on the market.

With so many people feeling they have been given a raw deal, some retirees may want to cash in their annuity believing it will get them out of a poor-value contract. However once sold on again, the retiree would lose even further value from their retirement cash as companies buying annuities will be looking to make a profit and will not offer the seller its true value, experts claim.

Pensions experts fear that these same people who have missed out on a good deal first time round could lose out yet again by selling the annuity on for considerably below its value.

Any money withdrawn from a cashed-in annuity would also be eligible for income tax, so anyone who takes it all at once could face an income tax bill of up to 45 per cent.

Knock, knock: The Pensions Regulator has refreshed its 'scorpion' campaign to alert retirement savers and pension scheme trustees to the risks of people being tricked by out of their money by cold calls

Yet again fraudsters could try to take advantage of vulnerable people by offering paltry sums for these valuable incomes.

HOW MUCH COULD I SELL MY ANNUITY FOR? You will probably be offered a fraction of what you would have earned if you had kept the annuity for a typical life expectancy. Fidelity Worldwide Investment predicts a 75-year-old who turned a £100,000 pot into a £7,000-a-year income ten years ago would be offered £48,000 – just seven years of income. If they are ill, this could fall to £35,000 – just five years of income. However, if they lived until they were 100 and kept their annuity, the same person would receive £175,000 over 25 years. This is almost four times the amount a healthy person would be offered as a lump sum had they sold their annuity. To get a good deal you would have to live for a considerably shorter time than the company that buys your annuity expects.

Richard Lloyd, of consumer group Which?, said: 'Pensioners who've been ripped off in the past must be properly protected from a second rip-off if they decide to sell it.' Andrew Tully, of pensions firm MGM Advantage, said the idea is 'full of pitfalls', and pensioners who were sold a poor-value annuity may be offered a poor-value cash lump sum. 'Two wrongs do not make a right,' he said.

Steve Webb added that retirees must be on their guard against fraudsters trying to trick them out of their savings.

'We are taking tough action along with our partners to tackle this scourge, but people must be vigilant,' he said. 'To get genuine guidance on your options, people should contact the free and impartial Pension Wise service.'

'If you are cold-called by someone offering you a free pensions review, it's probably a scam so put the phone down,' he added.

The Pensions Regulator's chief executive Lesley Titcomb said: 'The people behind pension scams are often agile, sophisticated and organised. Whatever the law is, they will seek to exploit it - so we expect the scams we see to continue to evolve in light of the new flexibilities available.