Which Is Cheaper Internal Combustion or Electric Cars?

Internal combustion engines are over 100 years old. They are very inefficient, at up to 30%. Electric vehicles are an emerging technology and are more efficient, at up to 6)%. Which though is cheaper - internal combustion or electric cars?
There is 35.8 Megajoules of energy in a litre of diesel, costing £1.20 (2017). Only 10.74 Megajoules of this energy is translated into useful energy at the wheels - about 10.74gajoules per litre.
Assuming the charging of an electric car is 85% efficient, We will need to supply    of electrical energy for the car to have the same useful energy as a car with an internal combustion engine.
In 2017 1 KWh electricity cost about 13p. A KWh hour is equivalent to 1000 W supplied for 3600 s, or  
21.61 Megajoules energy is equivalent to    which would cost 78p.
Hence electric cars are cheaper to power.