I believe EuroVelo signage is actually being installed in the UK at a moderate rate now. Sustrans has a new design of sign saying “For [EV12] follow [1]” which is going in every few miles in some areas. I’ve not seen any in the flesh but the photos keep cropping up in the NCN Facebook group, and here’s some on SABRE.
On the original R1 issue, apparently it’s signposted in Germany, Poland and Estonia.