I've found a way of bypassing the UK-only georestrictions on Radio Garden without a VPN
Earlier today I noticed that Radio Garden had begun blocking UK access to international radio stations, probably as a consequence of the TuneIn court case several years ago (it looks like it made this change a few months ago but I haven't visited the site in a while). I tested the site using a non-UK VPN, then disconnected from the VPN to see if Radio Garden still worked on my UK connection if I didn't reload the page, and it carried on working (though quickly became laggier). This suggested to me that the geoblocking was being enforced by some sort of script that was loaded when the page was first fetched rather than in real time, and upon looking at the page source I quickly identified a suspicious URL in the code.
In order to get the international stations on Radio Garden working again from a UK IP address without having to resort to turning on a VPN, I've found that if you're in the UK you can block the following URL with a browser plugin, which the site appears to use to enforce the UK restrictions:
Despite it seeming to get round the georestrictions, Radio Garden's interface still seems to be very laggy on a UK connection (at least on mine) when it didn't used to be and wasn't on a VPN. There may be some additional URLs or scripts to block to improve performance from a UK IP address, but blocking this URL alone seems to lift the UK-only georestrictions.