The party already advocates a 1% tax on homes worth more than £2m, but party president Tim Farron said those worth more should face an even higher rate, according to the Daily Mail.

He said: “You could have various rates within the mansion tax. A £4m property, for example, paying a higher rate.”

A tax on expensive properties is also backed by the Labour Party, suggesting it could become a reality if the two parties form a coalition after the next general election.

Farron told the Evening Standard he wanted to charge people who had properties and wealth at much more than £2m ‘a higher proportion’ instead of lowering the threshold to catch more properties.

He said: “I do take the point that in London there are many homes that are worth a significant amount of money which would be seen as not exorbitantly luxurious properties.

“It’s important that taxation should be progressive.

“You could have various rates within the mansion tax – a property worth £4m, for example, paying at a higher rate, as well as a higher global sum, than those with smaller properties.

“There is a way of doing this without damaging people who are potentially in a more marginal position.”