U.K. investors will no longer be able to add crypto exchange-traded notes (ETNs) to their tax-free individual savings accounts (ISAs) after the start of the new tax year on April 6, the Financial Times (FT) reported on Wednesday.

The tax authority, His Majesty's Revenue and Customs (HMRC), will reclassify cryptocurrency ETNs as qualifying instruments only for Innovative Finance ISAs (IFISAs), rather than the more mainstream stocks and shares ISAs.

ISAs allow users to put away up to 20,000 pounds ($27,000) a year without paying income tax or capital gains tax on the returns. The two main types are cash ISAs, bank account-like investments that pay interest, and stocks and shares ISAs, which invest in equities and exchange-traded instruments.

The Financial Conduct Authority's decision to lift the ban on retail investors accessing crypto ETNs last October was seen as a major development in the adoption of cryptocurrency investments in the U.K., as it raised the possibility of the vehicles being added to everyday products like ISAs.

Limiting them to IFISAs means this opportunity will be snuffed out because no mainstream investment platforms offer them. IFISAs are a somewhat obscure investment wrapper, offered largely for purposes of peer-to-peer lending and crowdfunding. None of the 57 platforms currently authorized to offer IFISAs have plans to support crypto ETNs, according to the FT's report, depriving investors of the tax shield that ISAs provide.

Investors who already have crypto ETN holdings in their ISAs will not be forced to sell them, however, as doing so "could risk some level of market disruption," HMRC said.

The authority said the ruling was due to crypto ETNs' "innovative nature and the fact that is an emerging market," and it would keep the decision under review with a view to including them in stocks and shares ISAs at a later date.

The decision risks positioning the U.K. as an outlier among major financial markets, where exchange-traded products (ETPs) have opened the door to crypto investment for a much wider base of users because they remove some of the technical aspects such as needing to deal with crypto exchanges and wallets.

George Bauer, Fidelity's head of investment and product for global platform solutions, said the government's approach "challenges the intention of allowing regulated access to crypto assets," the FT reported.

"We would encourage the government and HMRC to reconsider this and allow access through stocks-and-shares ISAs which are much more widely used."

HMRC did not respond to CoinDesk's request for comment.