Yesterday, the Treasury-owned savings bank said that it had accumulated £38.3bn in the first six months of the financial year as older savers deposited cash, with £23.8bn raised between July and September.

The figures mean that NS&I has surpassed its official £35bn target for the financial year.

The bank is given government-imposed limits each year on the amount that it can raise to ensure it does not enter into direct competition with commercial banks.

In July, in recognition of the unprecedented number of savers depositing cash, Chancellor Rishi Sunak hiked its target for 2020-21 from £6bn to £35bn - highest it had been given.

The target gives the bank £5bn leeway, so it can raise a maximum of £40bn, The Times reports. 

As a result of the mass influx of investment, NS&I suggested that it may have no choice but to slash rates further on its accounts, or to close some to new entrants, as it tried to stem the inflow of cash.

A spokesman said: “We always monitor the products that we have on sale and the interest rates that we offer and recommend changes to the Treasury as and when these are necessary.”

Last month, NS&I announced rate cuts affecting 25 million customers as it tried to slow the flow of cash being deposited and to encourage customers to consider taking money out. With an average customer age of 55, NS&I savers are known to be attracted to the safety net provided by the bank, which guarantees 100% of savings.

As of next month, 186,000 income bond accounts, with an average balance of £117,200, which will have interest cut from 1.16% to 0.01%. NS&I’s 172,000 direct saver customers, who have an average balance of £106,000, will have rates cut from 1% to 0.15%.

The bank has seen huge rises in the amount of money being put into accounts compared to last year. A total of £23.8bn was deposited between July and September, compared with £2.9bn in the same quarter last year, while the £14.5bn it took in the first quarter was in comparison with £2bn in the same period the year before.

Despite cutting interest rates from November 24, further cuts could be made, notably to its Premium Bonds, where the prize rate is dropping from 1.4% to 1% but could be cut further. There are 21.1 million Premium Bond customers with a combined balance of £88.5 billion.

Other accounts have lower to go, including five-year guaranteed income bonds where rates will be 0.51% from next month. A total of 47,000 savers have £3.4bn in these accounts.