All I know is the car suffers badly as the engine is so underpowered.
Apparently MG are very aware of this but couldn’t get the various 2.0 litre engines they buy in to meet new emissions regs.
They had to therefore reluctantly release the HS with the 1.5 unit as the GS had finished its production quota.
They are however in discussions currently for supply of a 1.8 unit that may be in the car by October.