I'm a Yank, not a Pom. So, I'm not up on all the latest electrical Euroregs. However, I'm GUESSING that 13 amps may refer to the maximum current rating for the plug itself.
There should be a label on the sauna stating it's current draw. Or perhaps, the current draw for the sauna is in the operator's manual.
If the stated current draw for the sauna is less than 10 amps, you might be good to go. Check local regulations, you might be required to install a dedicated electrical circuit for the sauna. Now, ten amps is the TOTAL current that can be safely drawn from that one residential electrical supply circuit. If you have other electrical devices plugged into that circuit the sum total of their current draw must be added to that of the sauna. Your options depend on your local electrical codes.