They can turn off their motors without losing any efficiency (which is why hybrids do so well on efficiency in city traffic). Depending on how slowly the traffic moves there will be a point where it is cheaper to stay in traffic (with the motor off x% of the time) compared to paying for parking.
Why the assumption that electricity for vehicular use will be taxed at the same rate as for domestic use when there's wide-scale adoption of electric cars? Red diesel, for agricultural use off-road, certainly isn't taxed at the same level as road use diesel in the UK.
They can turn off their motors without losing any efficiency (which is why hybrids do so well on efficiency in city traffic). Depending on how slowly the traffic moves there will be a point where it is cheaper to stay in traffic (with the motor off x% of the time) compared to paying for parking.