Interesting.
I guess an analogy could be that of a motorist driving at 10 mph over the 70mph limit. If that's all he/she is doing plod may not chase, stop, and book them. But if he/she is also on the 'phone, or not wearing a seatbelt, they may get booked for both offences... (Even though the speeding appeared to be "condoned" through inaction)
In the area we're discussing (LCY zone) you're going to be painted by quite a few radar I should imagine, so should the desire or need arise I suspect the CAA could very quickly ascertain that, for at least part of your transit, you were in breach of Rule5/land-clear.
2000'AMSL and the engine stops, you're going to be at 1900' before you've cleaned-up, achieved best glide etc.
Glide ratio of most spam-cans is what, say, 10:1? So you've got a 3nm window to put it down (at best).
I think if you gave them (CAA) reason to look, they'd probably find the answer they wanted
That reason may be a MOR for busting (laterally) the LHR/CTR, or it may be because of a forced landing, or it may be because the CAA just happened to be monitoring that day. (LFAT IFR arrivals spring to mind
)
No good saying ATC cleared you through - the buck stops here, in the left hand seat.