This letter, by John B Hart was sent right at the last minute of Harry's court date. Basically, the last moment possible in his quest to justify his own security detail while visiting the UK. John states there was sufficient evidence to arrest two people arrests for reckless endangerment. This does not mean high-speed chase, just bad driving.
The New York Post are saying that two arrests were not made, and that this letter was "sent in error".
Basically, this is a VERY convenient letter.