Kawasaki Triples Club

On October 1st 2014 the paper tax disc is obsolete.
There are other changes too,

https://www.gov.uk/government/news/vehicle-tax-changes

From 1 October, when you buy a vehicle, the vehicle tax will no longer be transferred with the vehicle. You will need to get new vehicle tax before you can use the vehicle.

You can tax the vehicle using the New Keeper Supplement (V5C/2) part of the vehicle registration certificate (V5C) online or by using our automated phone service - 24 hours a day, 7 days a week.

Alternatively, you may wish to visit a Post Office® branch.

Or alternatively, you may just wish to buy the bike/car, insure and drive it home anyway....It takes time to appear on the ANPR register once the PO has cancelled the disc, especially if he does not cancel it until you are home (ie does it next day)