More Coventry residents are challenging their council tax bills, figures reveal.
Think tank Bright Blue said a rise in the proportion of successful challenges across England shows that the country's tax system has "long passed its sell-by date".
The Valuation Office Agency – which gives the Government property valuations and advice – received 150 challenges from Coventry residents over their council tax bill in 2020-21.
This was up from 140 the year before.
Of the 140 challenges resolved last year, 30 (21%) resulted in the occupier's council tax bill decreasing, and 100 in no change – though some of these may have been submitted in previous years.
Across England and Wales, 40,620 challenges were launched last year – down from 43,650 in 2019-20.
Of the 38,070 resolved disputes, 11,670 (31%) resulted in the council tax band being decreased – up from 29% in 2019-20.
Just 40 households saw their council tax band increase.
All homes are given a council tax valuation band by the VOA based on its value in April 1991 – these range from the cheapest band A to the most expensive band H, with band D the most common.
Bright Blue said the rise in successful challenges is evidence that England's domestic property tax system is out of date.
Joseph Silke, communications officer at the think tank, said: “The banding system devised three decades ago disproportionately burdens those with more modest means.
“If the Government wants to level up, council tax and stamp duty should be entirely replaced with a fairer annual proportional property tax.”
There are three ways households can contest their council tax, with proposals – formal challenges that do not require evidence – the most used across England and Wales last year, at 57% of all challenges received.
If the VOA rejects this, an appeal (responsible for 7% of challenges) can also be made.
Taxpayers can also bring a potential inaccuracy to the VOA through a band review, though they do not have the right of appeal.
The Institute of Economics Affairs said the council tax system is too vulnerable to "arbitrary" challenges by individual households which can affect a lot of people.
Andy Mayer, IEA chief operating officer, said: "Often one person’s appeal triggers the revaluation of a whole group of homes, leading to further appeals.
"Pandemic restrictions have made this more difficult, leading to a backlog of cases.
"At some point the whole system will need to be rebooted, and potentially replaced."
The Ministry of Housing, Communities and Local Government said it has no plans to reform council tax.
An MHCLG spokeswoman added: “We are providing councils with £670 million of new grant funding to enable them to continue reducing council tax bills this year for those least able to pay.
“We have allocated over £12 billion directly to councils in England since the start of the pandemic and we continue to keep the position of councils under close review.”