It was British until a short-sighted company sold it to the Japanese, the EU at the time was also looking in the other direction too.

While ARM Holdings is based in Cambridge, England, it is majority owned by SoftBank Group which is a Japanese investment conglomerate.

What's important in the context of a European "sovereign computing" initiative is the licensing of the instruction set architecture. Like x86, ARM is still proprietary, while RISC-V is a free and open standard.

Others have already talked about the Japanese and Suadis.

My point would be that it has already been demonstrated that you can lose access to ARM technology as a consequence of US sanctions.

ARM is not a sufficiently independent ISA to guarantee sovereignty.

With RISC-V, you may lose access to a specific core, chip, or supply chain. But your ecosystem can pivot to an alternative. Long-term, you have the option of complete in-sourcing.

So, even working with Chinese chips and boards today can be progress, as long as more domestic RVA23 options can be expected to arrive later.

It is if you define the UK being in Europe (the continent). It isn't part of the EU as of today, although there's a good chance it will be again in the future.

Even though it's Japanese-owned most of their R&D still takes place in England.