The problem isn't the retailer but the couriers. I know somebody who works for a courier and she told me the following.
Since last friday the york depot of a major courier was not accepting any more trunking deliveries in and just turned them around each day unloaded as they had enough back log of parcels to deliver before Christmas.
UPS since Tuesday morning has still been collecting parcels but internally they will not deliver them before Christmas but are neither telling customers or the supplying company this even if the parcels are meant to be next day.
I found this out and actually stopped UPS collecting a parcel I had ordered on Tuesday and used another courier to collect it who delivered it two days later despite I had to pay for that courier and I never got a postage refund from the retailer.