Here is the DVLA advise regards the tax disc , the reason i know is mine arrived without a tax disc.
Background
Historically, motor dealers have provided customers with a tax disc on the sale of a newly registered vehicle. Changes in the operational processes of the Driver and Vehicle licensing Agency (DVLA), and the closure at the end of 2013 of the DVLA Local Offices that administer tax discs, mean that dealers will no longer be able to supply tax discs. This means that new vehicles may not have a tax disc at the point of collection by the customer.
What this means for customers
From the date the vehicle is registered it can be driven for 14 calendar days without displaying a tax disc. The disc will already have been purchased at the point of registration and will be posted by DVLA to either the dealer address, the address of the registered keeper or the address of the fleet operator.
The legislation
The display of a tax disc is governed by Section 33 of the Vehicle Excise and Registration Act. It is this section which has been changed, by legislation in the Finance Bill 2013, to allow for the non-display of a tax disc for 14 calendar days from the date of registration.
If the tax disc has not been received within 8 days of the date of registration, DVLA will provide a free duplicate. Registered keepers who have received the V5C can visit one of 400 Post Office® branches to obtain a free duplicate. From 24 June 2013, you can check which Post Office® branches will offer the service by checking online using http://www.postoffice.co.uklbranch-finder If you are a dealer or fleet operator and you are expecting the disc to arrive at your premises or you are the registered keeper who has not received the V5C, you will need to contact DVLA on 0300 7906802. All customers in Northern Ireland who have not received their tax disc after 8 days
Dealer was ready but its the leasing company who insist.
