"The dealer should have given you this and a trip to the post office with this, a valid insurance cert and MOT would have resolved this."

With all due respect, the OP does state in his original post that the insurance documents haven't arrived yet so he couldn't take a document that he does not have to the post office.

The only mitigation to DVLAs pound of flesh is the tax owing by the OP is small. A tax disc bought now or in a day or two will cover the untaxed period it was in the OPs ownership.

In this case, although the OP will have to pay the storage and release fees - DVLA will get poke all more back from him since the tax liability will be covered the moment he taxes the car and the amount of a fine for a few days untaxed won't begin to cover their expenses. Indeed, they'll try to get back tax for when the OP was not liable - so watch it.

Obviously shooting at the former keeper and caught someone who although guilty, is very small beer.

Keep ALL paperwork, and copy anything you send off. I hope you have a receipt.

But you also have some expert anwers here also in response to your duplicate question:

forums.pepipoo.com/index.php?showtopic=71364

For how long was the car untaxed? Strikes me he would be quite unlucky to be towed "instantly", judging by the number of apparently untaxed vehicles seen lounging about. So, how about a timeline for this?

You have 5 days in which you can continue to display the old licence while you wait for the new one to arrive, the 5 days only applies to disks bought on-line before the expiry date and is there to allow for postage delays.

If you do not buy a new disk before the old one expires and you continue to use it on the public highway yoau are guilty. If you buy a car that is not taxed and use it on a public higway before taxing it you are guilty.

In 38 years of driving I have never failed to tax my car thus I have never been fined or towed. Why should the law breaking scum get away with it. I say tow and crush their cars.