Personally I would print off the e mail confirmation that I had paid, prop it up in the windscreen and go.
Any ANPR checks are going to show your car taxed, and any officer looking would see you have paid.
Note that although Ethel's link shows that an offence of not displaying is being committed, it is phrased in a way that suggests you might consider taking the risk.
Oh yes they have, Panic Button. Simply because somebody who is not displaying road tax on the vehicle that has road tax could be displaying it on one that doesn't.
I'm sure you are right Ethel, but Rojash you have it right on the button.
However I would hope that the Police use their noddle on seeing a car two or three days out of date, and proof of payement displayed that they are dealing with a law abiding citizen.
I note in the thread you link to that someone did indeed have a rap on the knuckles but no fine, from a sensible policeman.
However I just taxed one of mine on line. The disc arrived on time. If it did not, it would not have stopped me using the car. I would simply print off proof and put it behind the out of date disc.
Since most people are caught using numberplate recognition, and my car was taxed, I think it very unlikely I would have had a problem.
you can drive the car if you want but you can still get a failure to display fine. the car is legally taxed which the police will check before issuing a failure to display
Sorting your car tax out online is not such a good idea.
Somewhere in the dark recesses of the Sorting Offices are some unscrupulous persons who are purloigning them.
The dvla are aware of this yet they still encourage us to do it online.
It is an offence not to display a tax disc even if you have paid for it and you will get a ticket because that will then register as a crime committed/solved in their statistics.
Three times over the years I have had tax refused by different jobsworths at a post office counters, who find fault in the date of insurance or MOT certificates. Some of these have contradicted each other on whether I need one for the day I apply or for the day the tax comes into force.
One year I had a certificate for the entire year from the day the tax was to start, but this wasn't good enough as I didn't take in the current one covering the day I was applying. Another year I took the current one in, but this wasn't good enough as it didn't cover the year I was taxing the car for.
At least on line you don't have to cope with people who like to say no.