Its called courier owner driver I believe. There are forums dedicated to it. Payment is per parcel, with certain numbers "guaranteed". You need no meet certain insurance criteria, sometimes need to buy equipment / work clothing. Not an easy way to make money.

Yodel offer 50-85p per parcel: http://codforum.org.uk/forums/viewtopic.php?f=2&t=11911 Amazon Logistics in the UK: http://codforum.org.uk/forums/viewtopic.php?f=2&t=11936

There is also lifestylecouriers.net for anyone who wishes to delve deeper into Yodel, co (requires registration)