The government has confirmed a 22% charge on interest paid on cash held within Stocks and Shares and Innovative Finance ISAs, part of a set of anti-circumvention rules published by HM Revenue and Customs on 23 June 2026.
The measures underpin the cash ISA reforms announced at the 2025 Autumn Budget and are designed to stop savers sidestepping the lower cash ISA limit that takes effect from April 2027.
The charge is one of three rules confirmed in HMRC's tax update. Alongside it, the government will prevent savers under 65 from transferring money out of non-cash ISAs into cash ISAs and will bar ISAs from holding 100% in money market funds.
Taken together, the rules close the routes through which an investment ISA could be used to shelter what is effectively cash or a ‘cash-like’ investment.
Why the rules exist
From April 2027, the annual cash ISA allowance falls from £20,000 to £12,000 for savers under 65.
The overall £20,000 ISA allowance is unchanged, so anyone wishing to use it in full will need to put at least £8,000 into Stocks and Shares or other non-cash ISAs. Savers aged 65 and over keep the full £20,000 cash allowance.
The government has framed the reforms as part of a wider strategy to build a retail investment culture, rather than as a revenue-raising measure.
The concern the anti-circumvention rules address is straightforward: without them, a saver could hold cash, or cash-like money market funds, inside a Stocks and Shares ISA and carry on much as before, leaving the lower cash limit with little practical effect.
The 22% charge on interest, the transfer block and money market fund restriction are intended to prevent that.
What is still to be confirmed
HMRC has said further detail will follow in its next Tax Free Savings newsletter.
Several practical points are not yet settled, including how the 22% charge will be administered and reported and how "cash holdings" will be defined for the purpose of the charge. The precise scope of the money market fund restriction is also unconfirmed.
It is worth stressing that money already held in a cash ISA is not affected. The lower limit and the associated rules apply to new subscriptions from April 2027, not to existing balances, which remain sheltered.
What it means for savers
For savers under 65 who have relied on cash ISAs to shelter larger balances, the reforms narrow the room to do so from April 2027. The anti-circumvention rules mean the obvious workaround is unlikely to be available.
Those aged 65 and over are unaffected by the lower cash limit. As with any change of this kind, the right response depends on individual circumstances and there is time to consider it before the rules take effect.
If you have any questions about how these changes might affect your savings, don’t hesitate to get in touch.