NIP does not have to be sent in 14 days, it's a general rule, but they can and do routinely get around this, generally they meet the target, the COURT makes the decision on any error in procedure should this be a point, courts genrally side with police/cps.
A lot of people relied on the "right to silence, so as not to incriminate oneself", but a recent high court case has seen this "right" killed, that is how they get you under 1998 rta, so this is longer any good.
I was discussing this very point last night with a friend/motoring solicitor.
marymonson.co.uk have a informative website.
tabetha