The best bit of advice I had from a solicitor is to not fuel the fire, politely respond to the CAA, saying your not aware there was an infringement, however could them supply further information. Also be sure that in addition to rule 5, you can demonstrate that there was a suitable open space in the event of an engine failure!
I had a letter from the CAA legal department a number of years ago based on a MOR filled by myself and ATC, it related to an inflight emergency, it came to noting. It was like many 'legal letters' purely speculative!