So, it seems that I've managed to have something delivered 2 weeks before it was ordered.

I had a chat with the Amazon agent - transcribe follows

You are now connected to Aiyswarya from Amazon.co.uk.
Me: Tracking info says that package was delivered 2 weeks before I ordered it.
Aiyswarya: Thank you for contacting Amazon.co.uk. My name is Aiyswarya. May I know your name, please?
Me: my name is Martin (as should be given on account)
Aiyswarya: Hello, Martin.
Due to an error the tracking information of the City Link is given as delivered.
In this case, I will contact City Link to deliver your parcel as soon as possible.
Me: tracking information is given the wrong tracking number. Therefore I cannot track the package.
Can you please have the information updated with the correct tracking information
or provide the correct tracking information to me.
Aiyswarya: I've checked the tracking information of your order and it states that your parcel is still in transit.
In this case, I will contact City Link to deliver your parcel as soon as possible.
As soon as we hear back from them we will update you via email.
Me: To check the tracking, you must have the tracking id?
Aiyswarya: Your tracking ID is <redacted>
Me: using that tracking information - that syas the parcel was delivered on the 12th December. to London
that was 2 weeks before I placed the order.
Aiyswarya: 27/12/12 18:38 Details of the consignment have been received from the consignor, but the collection Depot has yet to scan any goods.
12/12/12 16:59 These goods have been successfully delivered.
Me: So, my package has travelled in time?
Aiyswarya: Yes
You will receive your parcel on the estimated delivery date.
Me: but it says It was delivered on the 12th - I didn't receive it.
You've just confirmed that it's a time travelling package :)
Amazon Yesterday shipping :)
Aiyswarya: Yes you are correct.
I understand your concern that the tracking states it was delivered on December 12, 2012.
Due to an error the City Link information was incorrect.
Now the issue has been resolved.
The current tracking information states that your parcel is still in transit.
I hope that you will receive your order on estimated delivery date, that is December 28, 2012.
Is there anything else I can help you with?

So, it seems that I've had something delivered by Amazon Yesterday Shipping