Will Class C for LHR make any practical difference (serious question)?
Currently, UK Class D is being operated like US Class B.
Most European Class D is operated like US Class C but some (the busy bits) is operated like UK Class A.
In the US you can enter C with just a 2-way radio contact (and a Mode C transponder) so - short of some emergency taking place - you cannot be refused entry. In Europe, VFR traffic can always be refused entry.
Of course none of this is relevant to a nav error and a bust.
Re the 72 mile leg, yes, no problem if you are taking fixes along the way. However, it's not easy to find a 72 mile straight line which has unambiguous ground features all the way, say every 10nm.