Clicking behind glove box in foot well when starting or in reverse

That is the actuator clicking. This is pretty normal for these when they fail. Basically the computer stops the actuator when it sees the resistance in the circuit go up due to it reaching the stopping point. When they plastic gears inside the actuator strip, it never reaches that point of resistance so it just starts clicking like that.

https://www.2carpros.com/articles/replace-blend-door-motor

Unfortunately we don't have a manual on your vehicle to give you specifics but here are the instructions on a VW which is very similar.

Let me know if you have questions. Thanks

Unfortunately I am not familiar with parts sites in the UK (assuming this is where you are located). We are in the USA and while I can find multiple sites, I have no idea about the quality of their parts. I would recommend going to a local auto parts store and seeing if they can get it for you.

Sorry I wasn't able to provide more clarity on this.