Savers are making a final dash to protect their hard-earned money from the tax-grabbing clutches of Chancellor Rachel Reeves ahead of the Budget.

Record numbers of people have been piling money into tax-friendly Individual Savings Accounts in recent months to avoid the potential impact of a rise in capital gains tax.

It comes as it emerged a cap of £500,000 was previously floated by the now Chancellor in a column she wrote for The Independent in 2016.

And it's no wonder that these are the accounts of choice, given how many savers are becoming rich from the investment.

The number of savers who have built up a million-pound, tax-free nest egg by investing in stocks and shares has soared – trebling in the past three years. 

There are currently 3,180 Isa millionaires, up from 1,030 just three years ago, we can reveal.

The figures from HM Revenue & Customs, obtained through a Freedom of Information request by stockbroker InvestEngine, show there are more than 10,000 people who now have over £750,000 stashed away into these accounts while more than a quarter of a million have £250,000.

In the 2016-17 tax year there were just 570 Isa millionaires.

Fears of the looming tax raid have seen investors flock to stocks and shares Isas, funneling 156 per cent more into these accounts in September than during the same period last year, Isa provider Bestinvest has reported.

Payments into the platform in the first 11 days of October have already exceeded the amount paid in during the full month of October last year.

As well as stocks and shares Isas there are several different types of Isas – cash, junior and Innovative Finance.

Their big draw is that you can save up to £20,000 a year without having to hand over a penny of tax on the interest, returns or capital gains earned. 

This allowance can either go into one account or be split across multiple ones.

Their tax-free perks make them particularly attractive for those who would otherwise be caught out by savings tax or capital gains tax. 

But most millionaires have achieved the status by putting their money into investments, says Andrew Prosser, head of investments at InvestEngine.

It would have been impossible to reach the coveted £1 million mark by earning interest on cash savings alone. 

This is in part because interest paid on these accounts is significantly lower than the average returns you can achieve by investing in stocks and shares but also because the annual allowance for cash Isas has historically been lower. 

Between 1999 and 2008 you could only save up to £3,000 in a cash Isa, while you could stash up to £7,000 a year into stocks and shares Isas.

Prosser says: 'Even someone who has put the maximum in a cash Isa every year since they [Isas] were launched in 1999 would be at around £275,000 – a great sum, but well short of millionaire status. 

In contrast, more than 3,000 people have become millionaires through their stocks and shares Isa, and a further 30,000 have built up more than £500,000 for their futures.'

The average rate of return for a stocks and shares Isa over the past ten years is 9.6 per cent, according to rate scrutineer Moneyfacts. 

Meanwhile, lower-risk cash Isas have paid average interest of 1.21 per cent.

However, cash Isa rates have improved because interest rates have been higher. The average account currently pays 3.24 per cent, according to Moneyfacts.

Someone who saves the maximum £20,000 a year – £1,667 a month – in a stocks and shares Isa could become a millionaire within 19 years, by 2043, if they achieved the past ten-year average returns. It could take double that time to hit the million pound mark in a cash Isa, Prosser warns.

However, it has been possible to achieve even higher returns.

Investing your money in a tracker fund of global stocks would have earned you an annualised return of 12.77 per cent. But remember that any money you invest in the stock market can go up as well as down.

Prosser says: 'While not everyone will be able to put away this amount of money each year, it shows the importance of thinking long term with investments and the power of compounding.

'Getting started early each year, even with small amounts, and not leaving investing until the end of the tax year, creates the potential to grow large sums for later in life.'

It is rumoured that Reeves is likely to increase rates on capital gains tax, which would deliver a blow to savers whose investments are not within a tax-free account.