Can't speak for the UK, but in the Netherlands the tax deduction laws have changed (already 4 years ago) to no longer give lease-car drivers a tax advantage when driving a hybrid. Only full electric cars were eligible for a lower tax rate - the hybrids were taxed like regular ICU cars.

I have personally driven a C350e - a hybrid with an amazingly short range - and I really like the concept. If you compare the fuel consumption with similar cars (same, weight, size) it is much more fuel efficient. And indeed, that greatly depends on how disciplined the driver is. I charge wherever I can, manually set the car to 'full electric' until I run out of charge and don't "blaze around small roads at excessive speed". The 1600 kg Mercedes can run a comfortable 1 liter per 30 kms and more.

So sure, the fancy stories told by the salesmen, you are never going to see happen. But better fuel consumption without the charging stress (anyone seen the Tesla's waiting in line for supercharger-stations during the previous winter when we still were allowed to ski?) is easily done.