job of all these public bodies, equally, seeing as their salaries are paid out of the public's purse, is to get the airport and the public's needs met in a safe, efficient, sensible manner.
WHBM, you've answered your own question. That is indeed their responsibility. The CAA explained to Newquay what steps needed to be taken in order for them to achieve the required certification. That is the 'regulatory structure' in place under law in this country. The closure has nothing to do with the colour of ink on the safety case. Once the SC's have been signed off the CAA conduct an inspection of the airport in order to give it the final ok, they can't do that until they have all supporting paperwork (as required under law). The inspection is not a 'rubber stamp' exercise, they need to look at the safety features of the new equipment (lets not forget that most if not all the ATC equipment is brand new), I've attended a few of these inspections and the new equipment fails on around 50% of occassions.
The CAA have bent over backwards to help Newquay, but don't forget that there are many other airports trying to get major Projects across the line at the moment and Newquay have no right to exclusive support.