ASSUMING the Drayton is wired correctly. Blue is Neutral and should be connected to P1 as this wire is not used by Tado. The red wire is Live and should be connected to COM. The yellow wire is Switched Live and should be connected to NO.
If there’s a loose Earth wire you can connect it to P2. The P terminals are just used for parking unused wires.
If you’re referring to wiring up a hot water controller, there’s too many permutations to guess the function of the yellow wire and where to put it.