The chargers have been open to other EV’s for several months, you don’t need the subscription. All it does is give you a slightly cheaper rate, from what I’ve seen on the Skoda group you can get 42p/kWh charging off peak.
From Tesla site Q&A
Do I need a subscription to use a Supercharge?
No. Our Superchargers that are accessible to all EV owners do not require a membership. Supercharging Memberships are available for EV owners using the Tesla app to lower the cost of charging across the network. Tesla owners are automatically members.
https://www.tesla.com/en_gb/support/supercharging-other-evs#need-membership
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!