Pickup Policy Problem

Hello everyone. I am planning to buy a new Macbook any time soon in London. As I could see on the shopping checkout page, there is option for picking up the purchase instead of delivering it. Since I will be staying in London for a couple of days and I don't have an address to send the package, I would need to picking it up by myself.

My problem is that I need to make the purchase as soon as possible (credit card issues) but I won't be able to travel to the city until late December.

Does anyone know for how long packages are stored in Pickup Points?

What happens if I don't pick them up in time?

Thanks for your help!