@Gareth-Stockdale - If the suunto app is active and on the screen, then long press the central button to lock the buttons (will also lock the touch screen). you can still use the central button short press to change screen to any other additional tracking screens you have.
If for some reason you are running the app in the background and you want to prevent this, lock your touch screen (settings - display - and scroll down to touch lock, press it, then press OK).
You screen will revert to the ambient mode of your watch face, and you will need to hold down the menu button until is says unlocked to unlock your touch screen.