Hi Graham, welcome to the forum. I see this is your first post.
Here are two options: both will get you to Gare Hendaye (France), where you can either take the Euskotren or walk across the bridge to Irun.
1. The
no.3 Chrononbus, which takes about an hour.
2. Walk, bus or taxi to Biarritz station for a direct train (about 30 mins) to Hendaye.
Much will depend on your arrival time and how it fits with the bus and train departures.
A wildcard fun option would be to stay on the Chronobus until Hendaye Plage and hop on the
15 minute boat ride across the estuary to Hondarribia. You can start your Camino in Hondarribia or take a bus to Irun.
Happy planning