What do pies, poppies, and boats all have in common? They've all been used as slogans and metaphors by politicians who believe they can make society a better and fairer place.

Yesterday, Boris Johnson, donnedWore. a hard hat and dusted off his own favourite slogan, calling for the country to "unite and level up".

This morning, the political commentators are mostly agreed. A strong visual metaphor can help communicate a politician's vision. But what does 'levelling up' really mean?

Does the prime minister want to create a radically equal society in the tradition of the 17th-Century LevellersSomething that eliminates distinctions. In 17th-Century England, a group of Puritan extremists demanding equality for all people were known as the Levellers.? Or does he imagine society is like a computer game and he is going to help low-income families "unlock" skills and advance to the next level?

The vague language reflects a fundamental division in British politics between those who value equality of opportunity and those who think the problem is income inequality. And many think that, in order to win the next election, the prime minister needs to keep both sides happy.

In the post-war period, the gap between the rich and poor narrowed as governments redistributed wealth through high taxes and high spending. The chosen metaphor was the pie, and everyone deserved their fair slice.

This changed dramatically in the 1980s, when economists argued that if you "grow the pie" - and increase the overall wealth of the country - everyone will benefit. The rich should be given every opportunity to get richer. Or as Margaret Thatcher put it, "Don't cut down the tall poppies, let them grow tall."

Low taxes and pro-business policies began 30 years of economic growth in the UK and around the world. But inequality still rose sharply.

Despite the promise that "a rising tide lifts all boats", the wealth of the richest skyrocketed. Earlier this year, Oxfam reported that the world's 22 richest men have more wealth than all the women in Africa. Meanwhile, in the UK, the richest 1% has the same wealth as 60% of the rest of the country.

In response to these unprecedented levels of inequality, campaigners are calling for a Robin Hood tax or a Universal Basic Income to help redistribute wealth. But, yesterday, Johnson stood firm. "I'm not a communist," he insisted. He does not want to be seen as taking slices of pie away from the rich and giving them to the poor.

Instead, he believes the answer lies in levelling up the "left behind, neglected, unloved" in society by investing in building projects, priming the pump of the economy in the manner of US President Franklin Delano Roosevelt's New Deal.

Critics argue that the comparison is "fanciful" and far-fetched, and his policies are not on the same scale, or radical enough, to make much of a difference. Others say he is "ducking out" of a difficult debate about income inequality.

Research shows unequal societies are less socially mobile, making it much harder for the "left behind" to catch up with the richest in society. And the coronavirus lockdown has only accelerated the problem. With shops closed, the richest 20% in the UK have saved a total of 23 billion whilst lower-income families have exhausted their savings.

Yes, equality is unrealistic. Whilst we should not discriminate because of people's gender, race, or religion, it is undeniable that everyone has different skills and abilities. An equal society would not reward hard work and achievement, and would be poorer overall as a result.

No, equality is an essential political priority. A more equal society is a happier, safer, and healthier one. Moreover, income inequality and inequality of opportunity are closely related. The financial impact of the coronavirus pandemic will affect the poor much more than the rich. We need to launch a fight back at once.

Donned: Put on (an item of clothing).

Levellers: The political radicals emerged during the English Civil War and took their name from the practice of "levelling" the hedges put up by wealthy landowners to "enclose" common land.

Equality of opportunity: The idea that all individuals should be treated equally without prejudice developed during the 18th-Century Enlightenment and influenced the Civil Rights Movement and the modern concept of human rights.

Income inequality: The idea that wealth itself is the root of evil and a social problem appears in ancient Greek philosophy, Christian theology and, in modern times, the political thought of socialism, communism, and anarchism.

Both sides happy: In 2019, the Conservatives won a landslide victory by gaining the support of traditional Labour-supporters in the North and Midlands. These voters are more likely to think income inequality is a problem in the UK than traditional Conservative voters.

A rising tide lifts all boats: Although this aphorism (saying) is today associated with policies that benefit the wealthy, it was first used in 1963 by President John F Kennedy to justify funding large infrastructure projects.

Robin Hood tax: The idea of a tax on financial transactions gained support after the Great Recession (2008-9) and takes its name from the English folk hero.

Universal Basic Income: A radical idea for the state to provide all citizens with an income without having to work or claim benefits.

Priming the pump: A metaphor from engine mechanics, pump-priming in 1930s US involved creating thousands of government jobs to put money in people's pockets and kick start the economy.