Residents in Pembrokeshire will see the biggest increase to their council tax bills from April 2020 with a rise of 15.4%, according to the latest government data.
After collating the figures for every single local authority in England and Wales, Which? found that every council upped its rates for 2020-21, with 98 increasing them by more than the 4% cap recommended by the government.
There are 24 councils raising council tax bills by more than 5%.
The arrival of new council tax bills is likely to be particularly unwelcome this year, with many households adversely affected by the coronavirus pandemic, which has caused many businesses to pause trading or close altogether.
Here, Which? reveals how council tax increases vary across England and Wales, plus how the government plans to help those who are struggling to pay and extra tips on how to reduce your bill.
The average Band D council tax bill has increased by 3.9% across England.
The map below shows the percentage increases for council tax band D across England and Wales, using data from gov.uk and Stats Wales.
While there should be a cap of 4% this year - comprising a 2% council rise and an additional 2% for social care - some 98 councils across England and Wales are raising their bills by more than this.
The highest increase in England and Wales is in Pembrokeshire, which has seen a 15.4% increase. Band D properties in this area will be charged £1,252.41 in 2020-21, up from £1,445.22 in 2019-20.
Pembrokeshire has seen the biggest bill increases in recent years; last year, residents saw their bills go up by 9.97%.
Elsewhere, residents in Powys will see their council tax increase by 15.04%, and in Conwy it's 14.48%.
In fact, all local authorities in Wales are increasing council tax bills by 8% or more - rises that far exceed any councils in England.
In England, the biggest rise is in Wycombe - which, from 1 April will be merged into Buckinghamshire UA - where bills are going up by 6.84%.
The places with the biggest council tax increases still don't have the most expensive bills.
Those living in Rutland pay the most, with residents of Band D properties set to be charged £2,125.25 in 2020-21.
This is in stark contrast to the cheapest local authority of Westminster, where someone in a Band D property will pay just £781.99.
As for the smallest increases, those living in East Riding of Yorkshire will see bills increase by just 0.72%. Here, Band D property bills will change from £1,808 to £1,821.07.
Elsewhere, bills in North East Derbyshire are only up 2.19%, and High Peak residents will only see a jump of 2.31% for their council tax.
The government issued a press release yesterday (24 March) announcing a £500m hardship fund providing council tax relief for 'vulnerable people and households' during the coronavirus outbreak.
The fund will go to local authorities in England, so that they can reduce the 2020-21 council tax bills of working-age people who are already in receipt of Local Council Tax Support.
This will help households with lower incomes, but the amount of aid they receive will take into account the salary and savings of those living in the household.
Councils can also use the funding to support vulnerable people through local welfare schemes.
Hardship relief is already available for those who can't pay their council tax bills. It applies to those who are experiencing 'exceptional hardship' for reasons beyond their control.
To apply, you should contact your local council. The discount is applied at the council's discretion, and you may have to prove things like your income being less than your outgoings, having no savings, and having no other assets that could be used to pay your bill.
You might be able to get your council tax bill reduced if you are, or you live with, someone who qualifies for a reduced rate, or if the property you live in has changed since its council tax band was set.
Properties in England, Scotland and Wales are placed into council tax bands depending on their value on a certain date, along with their size and character, layout and location.
If you think your property has been placed into the wrong band, you can request a new valuation. This may result in your property being moved to a lower band, which would mean you'd pay less council tax in future, and get refunded for the extra amount you'd been paying.
However, it's also possible to be moved up a band, which could see your bills increase.
If you live alone in a property, you'll qualify for a 25% discount on your council tax bill.
However, you could also qualify for this discount if you or someone you live with counts as a 'disregarded person' for council tax purposes. This includes:
If you believe you qualify for a council tax discount, you'll have to write to your local council to make your case - it is not always applied automatically, and you may need to provide proof.
Councils may give discounts for second properties and holiday homes, but the kinds of discounts vary and they are granted at your council's discretion.
The likes of publicans and clergymen can get up to 50% off their second home when it's part of their work.
Council tax goes towards funding local services such as the police, fire services, parks maintenance, refuse disposal, street cleaning and services supporting the elderly and other vulnerable people.
Each council is responsible for managing its own funds. Expenses vary from council to council depending on the needs of its community, which is why rates can vary widely even between neighbouring councils.