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Fraudsters scammed nearly 49,000 older people across the UK in the past year, equivalent to almost six reports every hour, a BBC investigation has found.

The total number of reports has nearly doubled in the past three years, 5 live Investigates has learned.

But one expert said the true number of elderly victims was likely to be in the millions.

Police said more victims were coming forward but admitted they were the "tip of the iceberg".

Among those to have been repeatedly scammed is a farmer in his 80s from Norfolk, who has lost £450,000 over six years after fraudsters convinced him he had won £1.5m in a lottery.

His daughter-in-law, who asked not to be named, said: "They said all he had to do was send them an administration fee, it started small about £300 and then he should receive the money.

"But they didn't stop at that, obviously he didn't get his money and they kept ringing.

"It's gone out of all proportion since that initial contact."

Police and trading standards officers in Norfolk have been involved in his case but his family believes he is now "addicted" to his pursuit of a big-money payout and is still trying to send money.

"I think the scammers are absolutely evil," she said.

"But they are also very clever in how they do it and they make it sound very plausible, so much so that it sucked him in and probably hundreds of other people."

The 5 live Investigates team asked Action Fraud, the UK police's cyber-crime reporting centre, for a breakdown of the five most common types of frauds affecting older people reported to them over the past three years. It revealed:

in 2016-17 there were 40,487 frauds affecting people aged over 60 reported and 48,981 last year - equivalent to nearly six crimes every hour

this was up from 25,659 reports in 2015-16

last year 1,140 victims were aged over 90 and 13 were over 100

But Prof Keith Brown, of Bournemouth University, an expert who studies scams, claimed these reports represented as few as 5% of the true total.

"It's hugely under-reported - we're talking about millions of victims," he said.

"If this were burglary or street crime there would be a huge outcry, but it's hidden behind closed doors.

"Over the next few years this will become the next big scandal like the dawning realisation of the scale of child abuse."

How to report a scam

If you suspect you've been a victim of a scam you can visit the Action Fraud website.

Action Fraud can also be contacted by calling 0300 123 2040.

During 2017-18 so-called advanced fee frauds, which include victims being told they have won a lottery but must pay a fee to receive the prize, were the most common scams, with almost 20,000 cases - including 370 victims aged over 90.

Computer software service fraud, in which victims are told their computer has been compromised by a virus, was the second most common crime with more than 12,300 cases last year.

Prof Brown warned fraud costs UK consumers an estimated £10bn a year in losses, up from an estimated £4-6bn annually in 2016.

He added: "We're getting better at blocking mail scams coming through the post and the call blocking technology is improving, so increasingly fraudsters will turn to targeting their victims online."

Lara Xenoudakis, temporary detective chief inspector with the City of London Police, said more victims may be aware they can turn to Action Fraud for help but admitted the cases they saw did not represent the scale of the problem.

"Fraud is still very under-reported, the figures are only the tip of the iceberg," she said.

"People are embarrassed to report, they feel ashamed to have become a victim... there's nothing to be embarrassed about. Fraudsters are so experienced now and so believable, it is very easy to become a victim and it could happen to anybody."

5 live Investigates is on BBC Radio 5 Live, 23 September at 11:00BST - catch up on BBC iPlayer Radio.

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