I've always been a bit iffy about installing a 3 phase socket with only one phase connected.I would go for the 5 pin 32 amp tail instead of the 3 pin tail as the cost the same and you can use it if you plan to travel to areas off the beaten track where 3 phase 32 amp outlets are fairly common, I have never seen a single phase 32 amp outlet on Plugshare
If I ever go out into 3 phase socket country, I plan to get a 5 pin plug / 3 pin socket 32A extension lead made up, because those sockets aren't always conveniently located near the parking anyway and it'll function as both an extension and adapter.