You'd think they could go with the existing British Rail branding. The double-arrow logo is iconic and still in plenty of places.

And given that many of the private franchises took the names of prenationalization companies, it's hardly unprecedented.

Well they can't call it the United Kingdom Railways now the UK is falling apart.

Also, more precisely, it doesn't cover Northern Ireland, which is separate and has its own system linked to the Irish rail network.

https://en.wikipedia.org/wiki/NI_Railways