Quick update.
The below is a email response from MG UK.
I would love to know if anyone else experiences this, so I can put my mind at rest.
Once the EV battery has been depleted past 90% the engine can decide to put power back into the EV battery to extend the range and so the revs can jump to 3800 to charge the EV battery.
Two week old HS PHEV. We tested it out in EV mode and drove it until the battery ran out. At the 10% point there was no engine activity at all. The engine didn't cut in until 81.2 miles, when the battery was zero percent. At no time did it rise near 4000 revs, so I would regard your car as faulty.
When the car goes above a certain speed, the engine revs drop down considerably, so a second gear is definitely kicking in.
From the manual :-
Running-in
The engine, transmission, brakes and tyres need time to
'bed-in' and adjust to the demands of everyday motoring.
During the first 1500 km, please heed the following advice
so as to enhance the long-term operation performance of
the vehicle:
•
Do not allow the engine to exceed 3000 rpm in any gear
or the vehicle speed to exceed 120 km/h.
• Do not operate at full throttle or allow the engine to
labour in any gear.
• Do not drive at a constant speed (either high speed or
low speed).
• Avoid heavy braking where possible.
After 1500 km, engine speeds can be gradually increased.
