Savings rates for new customers have been tumbling since since the beginning of June, a MoneySavingExpert.com investigation reveals. This makes it more important than ever to search for the best rate amid plummeting returns.

Rates across standard savings and tax-free cash Isas are down for those looking for a new home for their cash. Within those categories, easy access and most fixes have also slumped. Commentators say the falls could continue.

Our research shows how the best buy deals have dropped massively, with the top, taxable five-year fix currently at 4.06% compared to 4.45% at the start of June (see the Top Savings guide for the best deals).

Savers have had to put up with rock-bottom returns for over three years with the Bank of England base rate stuck at its historic 0.5% low since March 2009.

To make matters worse, high inflation, which climbed last week to 3.2%, is further eroding the value of deposits. Once tax is deducted, most returns fail to keep pace with the cost of living.

And to compound the misery for savers, banks now have less incentive to raise cash via customer deposits — they often up rates to attract money — due to the new Government-inspired Funding for Lending scheme to help institutions raise cash to fund mortgages.

Slump could continue

Andrew Hagger, independent personal finance analyst, thinks the situation could get worse: "With an increase in base rate nowhere in sight, it's going to be a further prolonged period of misery for savers.

"Their cause won't be helped by the Funding for Lending scheme. Lenders will be able to borrow cheaper, which means they will have less need to attract funds from savers.

"There will be less competition to offer best buy rates, which will see rates drift lower over the next couple of months."

The tables below show how most best buy deals have dropped over the last three months (see the Top Savings guide for the best current deals).

Best buy standard savings (taxable)

Account type 1 June 1 July Today
Easy access 3.17% 3.2% 3.07%
1-year fix 3.6% 3.6% 3.6%
2-year fix 3.75% 3.75% 3.8%
3-year fix 4% 4% 4%
4-year fix 4.1% 4.05% 3.9%
5-year fix 4.45% 4.25% 4.06%

Best buy cash Isas (tax-free)

Account type 1 June 1 July Today
Easy access 3.35% 3.3% 3.06%
1-year fix 3.6% 3.5% 3.25%
2-year fix 4% 4% 3.6%
3-year fix 4% 4% 3.7%
4-year fix 4.15% 4.15% 3.8%
5-year fix 4.25% 4.25% 4.05%

Alana Fitzpatrick, MoneySavingExpert.com money analyst, says: "With savings rates tumbling, it's now more important than ever to check the rate you're getting. If it's too low, ditch it and switch away.

"Even though rates aren't great, it's still worth grabbing a best buy and aim to get at least 3% on an easy access account.

"If you can lock your money away for longer, consider a fixed account, where rates are slightly higher, though there's a risk other rates could rise while your money's tied up."