Lopez, I know you work for a courier company so probably know more about the state of play with couriers, as of April 2010, but 2 years ago, I went to parcelforce's website and booked in a parcel, for it to be collected and delivered. I did this 3 times and parcelforce were 100% reliable - collecting the package on exact date I specified on the website.
Basically, you make the booking online, make payment online and then print out the label. You then stick the label on the package.
On the day parcelforce arrive, they will scan the label/barcode and take the parcel away.
Note: these were 1-off parcels and I my order was not part of some bigger contract.