From the Post Office website:
UK arrangements
Scheduled collection customers
All services will run as normal for customers with scheduled collections, with deliveries up to and including 24th December.
The UK last send by dates for guaranteed delivery before Christmas are:
Next day services: 23rd December
Parcelforce 48: 22nd December
Please note, extended delivery speeds do exist for certain outlying postcodes. Please check our UK delivery speed exceptions page for details:
http://www.parcelforce.com/portal/pw/worldwidedirectory?catId=19300174&pageId=wwd_countryinfo&country=7
