"This scheme might have its cynics, but I have spoken to very wealthy people who want to help the borough more."
The Council hopes to collect a voluntary council tax supplement of £1,376 per property from April 2018.
If each household paid the charge, the Council would generate £2.75m in revenue which it says could used to freeze council tax for all other bands.
Westminster Council is currently lobbying Government to make the new council tax band mandatory, but is confident that people will pay the extra fee.
Leader of Westminster City Council, Nickie Aiken said: "This scheme might have its cynics, but I have spoken to very wealthy people who want to help the borough more.
"Westminster is home to some of the poorest and richest people in the country and some of the most expensive real estate in the world. But while there is a reality to the cost of living in a capital, this is a council and a Government committed to fairness. There is more we can do to help those who are struggling to pay the bills.
"One way of doing that is via a voluntary supplement linked to the top council tax band. There is no appetite from central Government to revaluate council tax, but we believe we have come up with a method which will allow the well-off to voluntarily help those just about managing."
Toby Whittome, Sales Director at Jackson-Stops London, commented: “Would you rather gift money to your favourite charity, or hand it over to the local council? This is the key question the efficacy of the voluntary ‘mansion tax’, or Westminster community contribution, ultimately comes down to. Many of the owners of £10 million+ properties in Westminster likely already make regular charitable contributions and I believe a considerable proportion will prefer to keep giving to charities as they always have done.
“There are also some practicalities that don’t seem to have been considered at this stage. With high net worth individuals more likely to travel or have other homes, how are people going to be reminded they could make this contribution? A quick email or letter asking for an extra donation? Band H properties for council tax purposes are classed as such based on their real or assumed value in 1991, but who’s to say in today’s fluctuating market which homes are worth £10 million or more?
“If the underlying goal is to increase the amount of council tax collected in London a sounder idea, guaranteed to succeed, is a small, incremental increase to the higher council tax bands across the board in the Capital which are currently fairly low compared to many other councils across the country. This is certain to secure additional funds for non-statutory services such as youth clubs, without the vagaries of a voluntary form of taxation.”
