Since the engine can always be operating (when running) at its most efficient load the fuel efficiency more than compensates for any additional weight due to batteries and electric motor.

As we all know, the early hybrids (now called mild hybrids or even self charging hybrids) use a much smaller engine so use less fuel. The tiny (relatively small) battery boosts the performance when needed.

My colleague was (and still is) a fan - he boasted of his 55MPG from his new hybrid some years ago when a typical petrol engine would only do 40MPG. I got 60MPG from my dirty diesel at the time, but he had paid a premium to even get that. His car cannot go above a few MPH without the engine on.

I call this a con, other folks may call it good marketing, either way it is not honest. But it is at least getting people used to the idea that electricity is going to be involved and allowing the motor industry to upskill somewhat whilst we install several million more chargepoints….

Those hybrids have a combined motor/generator and a small battery.

When a conventional car needs to slow down, the excess kinetic energy is turned into heat in the brakes, and wasted.  When the car needs to speed up again, it can only be done by burning more fuel.

A hybrid will use the generator in place of the brakes, to slow down the car and charge the battery.  When the car needs to accelerate again, the battery and motor can be used to give the car a push, requiring less fuel.

It's most useful in city driving.  On the open road, the hybrid system delivers little benefit.

Thank you for your replies but Andrew is correct when he states that small old cars with under 1,000 cc engines can be less polluting than almost all new fancy hybrids.

The mayor of London has just announced ultra low emission zone will  be extended to inside the north and south circular roads but electric vehicles will be exempt.  Not sure of hybrids? 

I hired a Fiat 500 Hybrid in France recently and was annoyed that there was no way of recharging the battery overnight and no way of turning off the engine in cities and just using the battery.  This is an outrageous omission and means that road-hogs can accelerate away from traffic light Ferrari style and let the engine recharge the battery at the next lights polluting the atmosphere terribly.  

Car manufactures should be forced to recall all hybrids are fit them with a change over switch to battery only, as car makers are promoting hybrids as containing an environmentally friendly engine. 

There are a significant number of ways in which a hybrid can achieve a big reduction in fuel consumption and perhaps more importantly CO2 Emissions. I can talk about the system that Ford and Toyota use (they use a common technology) I had both a Ford Kuga PHEV and a Kuga diesel. The PHEV was great, significantly better than the diesel even if I didn't charge it. Charging gave me a 30 mile electric range with a smallish battery. Not all hybrids run this way and so it does vary from manufacturer to manufacturer, although there are common themes. Biggest points are

1:  the Ford and Toyota Engine is modified to have a very long expansion stroke (an Atkinson engine), which extracts as much of the work as possible (similar to diesel expansion). This gives very good fuel economy at the loss of specific power (so the engine is a low power 2.0L, but the electric motor supports the acceleration, so whilst not a sports car, it is good) 

2: The hybrid gearbox operates as a CVT so you can run the engine at the most efficient point for any power level. 

3: At very low power levels when the conventional engines would be very inefficient the hybrid runs electric or worst case it runs efficently and charges the battery.

4: Regenerative braking. The better hybrids now run series brakes which means all but severe breaking is done by regeneration and energy recovery (also saves brake wear and reduces brake dust)

5: Also remember a litre of petrol has about 10% less energy content than a litre of diesel so a fair comparison is to expect 10% less mpg for a petrol if you want to talk efficiency. Sadly not reflected at the pumps so this point is often missed 

6: Further petrol has more hydrogen and less carbon than diesel so is slightly less poluting for global warming  (both are bad, but petrol slightly less bad)

As a slight note diesel gets better mpg than petrol due to expansion ratio, throttling loss (a diesel engine doesn't have to work hard against a throttle) and the fuel energy density.

The first two points get addressed by the full self charging hybrids and so the hybrid is the better option. I have owned both and will be staying hybrid whenever I can.

I agree that Atkinson engine and CVR rubber band DAF type gearbox are ideal for hybrids. But they must have a switch so that in cities ONLY the battery and electric motor are in use to avoid pollution and allow city runabout to recharge at home.

The mayor of London should give free only to EVS with the switch.

I can only confirm for the Ford but it already does (all their PHEV's do). You do need plug in capability to do this. It has 4 modes.

EV Auto : Lets the car decide when to use battery power when it is best (normally EV a default until teh battery starts to run low)

EV Now : Forces the car to run EV unless the battery is flat

EV Later : Runs the engine to preserve battery power (still gets excellant fuel economy for reasons I siad before)

EV Charge : If you have used the battery up and want more battery range later you can ask for charge mode, which will decide the most fuel efficient charging mode and charge the battery up. Good if you start in a city, run down the motorway to another city.

At the moment these modes are all switch selectable and its easy to do. 

I have ordered a Mach E Mustang as a company car with a ten month + waiting list so in the interim period I am driving a Toyota CHR 1.8 HYBRID, it delivers you the best of both worlds, city and traffic driving on battery and a joint battery and engine on the motorway, on one occasion I drove from London to Newbury on the M4 with road works all the way, when I arrived the instrument cluster displays a snap shot of your last MPG and the Toyota returned 78MPG, even at 70MPH and you take your foot off the pedal the battery kicks in, as for financial viability it is second to none, on average with my weekly high mileage I use a tank of fuel in comparison my own car is a Jaguar XF and for the same journeys I use two and a half tanks of fuel ( with a bigger tank) 

Until late last year I had a Mitsubishi Outlander PHEV.

The Outlander’s transmission is somewhat different to that described above. It is similar to that found in most normal BEVs. It has two electric traction motors, one driving the rear wheels, the second the front. Both are directly connected to single speed transmissions. As it is a hybrid it also has a petrol engine, directly connected to a generator and this can also supply power directly to the front wheels at speeds above 43 MPH.

The vehicle has three modes of operation: 

1. Full EV, only the battery supplies power to the electric traction motors.
2. Series Mode, petrol engine supplies power to the battery and traction motors.
3. Parallel Mode, at speed above 43 MPH, as series mode but also powers the front wheels though a clutch on the transmission.

On a motorway run, with minimal battery, I found it would switch between all three modes. When in Parallel mode spare power would charge the battery, enabling the car to fall back to EV Mode. Series Mode would also kick in from time to time as required.  As a driver I was only aware of this by monitoring a display, the car drove the same in all modes. The car would automatically decide which mode to use, though there were controls to make it save battery - kept the battery charge at constant level - to allow EV Mode at the end of a journey and charge to charge the battery from the petrol engine (generally to be avoided) and on later models a control to prioritise EV Mode.

On a full battery it was possible to do around 25 miles in Full EV mode, though the petrol engine could kick in for a number of reasons including:

• Hard acceleration
• Steep hills

(the petrol engine would start if more than 50% of the maximum power was required)

• Cold mornings - unless you turned the cabin heater off
• Going above (I think) 84 MPH
• If the petrol tank had not been refueled in the last 3 months - this caught me during lockdown.

The outlander is quite a big heavy beast, with the aerodynamics of a brick, my long term fuel consumption was around 85 MPG - during lockdown around 220. Motorway consumption was around 45 MPG.

I purchased the Outlander to see if I could live with an electric vehicle - the answer to that  clearly yes, with the smoothness of transmission (No Gears) and general ease of driving persuaded me I would never want to go back to an ICE car. Late last year I went the whole hog to BEV with a Hyundai Kona Electric, which has been nothing but a pleasure to own.