This is an area fraught with problems, not least because of the mythology surrounding it. It is difficult to be precise, when commenting on an individual case, because there are so many variables. Some caused by unlikely interpretations of the legislation put forward as fact in some parts of the internet, and some caused by the range of laws and amendments to laws which cover this sort of thing.
As far as the law goes a good place to start is here.
Quote:
Interpretation Act, 1978, section 7. References to service by post.
Where an Act authorises or requires any document to be served by post (whether the expression “serve” or the expression “give” or “send” or any other expression is used) then, unless the contrary intention appears, the service is deemed to be effected by properly addressing, pre-paying and posting a letter containing the document and, unless the contrary is proved, to have been effected at the time at which the letter would be delivered in the ordinary course of post.
The phrase "unless the contrary is proved", means that delivery is not an irrefutable consequence of posting, but rather a "rebuttable presumption". Thus giving rise to a defence of the NIP not arriving in time.
As a starting point in the absence of any other information
IF the car was registered in the name of the OP and
IF the address the DVLA have for him is the one he currently lives at then a delivery time of a month is probably too late for the delivery of the
first NIP.
He then has the chance to go to trial and prove, on the balance of probabilities, that the NIP took a month to arrive. Courts see lots and lots of these. Often people who have never complained to the post office about late or missing delivery. Often people who can show no correspondence with any other body about missing or late correspondence. In such cases it is down to the credibility of the witness.