https://www.gov.uk/government/publications/practice-amendment-notice-223/pan-223-the-classification-of-non-fungible-tokens-nfts-virtual-goods-and-services-provided-in-the-metaverse?utm_source=substack&utm_medium=email

This PAN is to inform customers applying for UK trade marks about the IPO’s approach to the classification of the above types of goods and services.
Along with many other registering authorities, we have seen an increasing number of applications for trade mark specifications containing these terms. We have also received requests for guidance on the acceptable ways in which these terms can be framed and the correct class in which they fall. This PAN aims to provide that clarity, albeit recognising that the terms are representative of new forms of goods/services in a fast-moving technological field; we aim to update this guidance as and when new developments arise.
NFTs were born out of the cryptocurrency networks. They serve as unique and unalterable digital authenticity certificates of ownership for virtual or physical assets such as art, collectibles and gaming. The Cambridge Dictionary defines an NFT as:
a unique unit of data (the only one existing of its type) that links to a particular piece of digital art, music, video etc. and that can be bought and sold.
As a token of data, the NFT consists of an entry on a blockchain. However, it is inextricably linked to the asset (normally a digital asset) to which it relates. The NFT is used, primarily, to represent the ownership of that asset, albeit not necessarily the ownership of any underlying IP such as copyright. For example, a unique piece of digital artwork or an audio file may be “minted” as an NFT, enabling the ownership of that digital asset to be proven and managed via the relevant entry on the blockchain.
Given the above, NFTs will not be accepted as a classification term alone. Without an indication of the asset to which the NFT relates, the term is inherently vague. However, IPO will accept the following type of terminology in class 9:
digital art authenticated by non-fungible tokens [NFTs]
downloadable graphics authenticated by non-fungible tokens [NFTs]
downloadable software, namely, [list the type of goods], authenticated by non-fungible tokens [NFTs]
digital audio files authenticated by non-fungible tokens
downloadable digital files authenticated by non-fungible tokens [NFTs]
The above guidance is in line with the 12th Edition of the Nice Classification which includes in class 9 “Downloadable digital files authenticated by non-fungible tokens [NFTs]”.
Whilst NFTs relate primarily to digital assets, it is feasible that NFTs can be used to authenticate anything, including physical goods. In light of this, physical goods clearly defined as being authenticated by NFTs will also be accepted in the appropriate goods class, for example: