Anything in that bbc article thatwasn't in quotes i will take with a pinch of salt. 50% increase in engine efficiency is madness.
Even if it was the whole package, those kinds of increases only happen with turbine power plants; with countless cycles feeding of the main power.
I'll expect maybe 10% to 15% in the best case. This is with loads of equipment bringing the cars hundreds of kg overweight that defeat the purpose of saving fuel in the first place.