"...are they in breach then?"
This is not my area of expertise, but my take, having read the statute, is "maybe".
The authority issuing the notice normally has 28 days to serve you with it. They must apply to the DVLA for the your details within 14 days. However, if those details are not provided in time for them to meet the 28 day deadline they have the power to issue a notice for a further six months after the 28 days have elapsed.
So you need to find out (1) did they apply to the DVLA for your details within 14 days and (2) when did they receive those details. If the answer to (1) is "No" they are not entitled to issue a notice. If the answer to (1) is "Yes" they have to show that they did not have your details in time to meet the 28 day deadline.
You really need to post your question in the "decriminalised" section of "Pepipoo":
http://forums.pepipoo.com/index.php?showforum=30
There are experts there who will give you a knowledgeable, definitive answer and tell you how to proceed if you have grounds to reject the notice.