HiThey now allow you 5 days from the end of the month to receive and display you tax disc if you have ordered it online from the DVLA. If you haven't taxed your van on the 1st of the month then you are breaking the law by driving it on a roadway.Edited after post.Copied from DVLA website. "I have not received the tax disc. Can I use the vehicle without the tax disc displayed?When you apply for a tax disc online or by using our phone service you are able to legally continue to drive your vehicle for up to 5 days after the tax disc has expired while you wait for the new tax disc to arrive. This will only apply when you have applied for a new tax disc before the current one expires. You should continue to display the expired disc on your vehicle, until the new one arrives."Spruce
If you have bought the tax it will show up on the police database as such.
put a note in your window -tax in the post -