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"We tend to have higher fuel prices than the Americans, so we prefer smaller, more fuel-efficient vehicles, while they generally prefer larger vehicles."

In recent years, the growth of UK international aviation emissions has actually been lower than that of passengers, which has been attributed to more fuel-efficient engines - yet it's unclear if this trend would continue with a third Heathrow runway.

An alternative option would be to consider catamarans, which are far more fuel-efficient than single-hulled ships.

For instance, some models may be long or heavy but still be fuel-efficient.

“Yes it tends to be the bigger the car the heavier it is and so it’s less fuel-efficient. But it’s a clumsy way of looking at it,” she says.