The financial regulator is finally cracking down on high street banks who have let a huge swathe of our savings wither away in scrapheap accounts that earn as little as 0.1 per cent.

Half of the nation's savings, worth £354bn, is housed in easy access accounts, but most consumers who hold onto the same account for years may not realise their interest rate has dwindled and that better-paying accounts have come onto the market.

That is because the big four banks, including two partly owned by the taxpayer, are keeping us in the dark about this two-speed savings market, according to the Financial Conduct Authority, which has identified a junkyard of 1000 accounts paying pitiful interest.

In its market study published this week, the FCA said big names had capitalised on their market dominance and consumer inertia to drive down interest rates on older accounts, with as much as £160bn held in products that paid less than the Bank of England's base rate of 0.5 per cent in 2013.

Of that amount, £145bn was kept in moribund accounts with balances of at least £5,000, making it a no-brainer for many to switch to a more attractive deal.

The FCA said the banking giants - Barclays, HSBC, Lloyds Banking Group and Royal Bank of Scotland - paid "materially" less than the rest of the market on easy access accounts, with many of their current account users lulled by the convenience of using the same bank for their savings.

The regulator has proposed speeding up the current 15-day timetable for savings account switching to make the process easier for consumers who perceive it to be too much "hassle". It will also expect banks to provide more information about customers' accounts and better options that may be available.

Anna Bowes, founder of the website Savings Champion, said: "Any savers who believe that there is little to be gained by switching in the current low interest rate environment need to be aware that they could still make hundreds, if not thousands of extra interest by moving. Switching is a vital part of getting better rates for savers."

Simon McCulloch, director at comparison website comparethemarket.com, said an "overly onerous and often jargon-heavy process" means consumers lack the time or inclination to switch, and "we need to see the banks playing fairer".

Building societies have come out fighting since the FCA's report was published. Brian Morris, head of savings policy at the Building Societies Association, said: "Not only are average interest rates higher at building societies, but savers in closed accounts are not disadvantaged relative to new customers."

He cited data from Savings Champion showing that 78 per cent of accounts at building societies topped the base rate throughout 2014, compared to 56 per cent of comparable bank accounts, while rates on 'closed' variable rate savings accounts were typically 0.06 per cent higher than rates paid on new accounts.

But the FCA's review may make for uncomfortable reading among challenger banks, hoping to break up the existing providers' monopoly. Only 26 per cent of consumers would pick a lesser known bank, even if it topped 'best buy' tables on comparison websites.

Edinburgh-based Tesco Bank offers a respectable 1.35 per cent on its instant cash Isa, while the Post Office offers marginally more - 1.4 per cent - on its online saver, though this rate will plummet to just 0.65 per cent after 12 months.

The FCA however said it would not intervene to stop such 'teaser' rates being offered to savers.