Drivers could be at risk of invalidating motor insurance by not declaring their car is fitted with a common feature that hundreds of thousands of vehicles have.

Car owners are being provided unclear information when buying cover via comparison websites, with the popular feature often hidden in fine print or part of vaguely worded guidance regarding what constitutes a modification when completing an online quote.

The item in question is a tow bar.

While there is no exact figure for the number of UK cars with one installed, the Caravan and Motorhome Club's one million members - and the number of people who need to tow horseboxes and boats - suggests there are hundreds of thousands on the road.

Auto Express said it had been contacted by a motorist who was left with a six-figure bill when his insurer refused to pay out on a claim and cancelled his policy because he had not listed his car's tow bar as a 'modification' when running a quote via comparison website Money Super Market.

There are now major concerns that vehicle owners across the country could unwittingly be driving with invalid insurance if they haven't declared the practical feature as a modification.

'We were contacted by a desperate driver after his insurer, Allianz-owned Flow, cancelled his policy following an accident on the grounds that he had failed to list his car's tow bar as a modification when purchasing cover,' explains Chris Rosamond, current affairs editor at Auto Express told us.

'He'd purchased Flow insurance via MoneySupermarket and selected the 'unmodified' option when applying for quotes because the website's help link did not mention tow bar as a modification.'

The price comparison site's wording in its pop-up help box in the modifications section of the online form states: 'What does this [modification question] mean? 

'If you or a previous owner has made a change from the manufacturer's original specification, such as alloy wheels, air conditioning, bodywork, exhaust system or tinted windows, add it here. 

'If you're unsure if your car's been modified, check its previous history to find out.'

Auto Express found rival insurance comparison websites' guidance on what constitutes a modification is similarly vague.

Others simply stated that 'modifications are changes to the car's original specification' and that these can be 'mechanical or cosmetic changes inside or outside the car'.

Rosamond says some comparison websites do not provide easy or obvious routes to information about whether a tow bar is a relevant modification to a car's original specification. 

Furthermore, he warns there is no obvious link to information about the potentially devastating consequences of not meeting the requirement to notify insurers about something as simple as fitting one.

'The driver who got in touch with us told us that he is at his 'wits end' adding that, following a routine vehicle collision, his insurer had refused to honour his insurance at the last minute, leaving him with a potential six-figure cost and incredible stress and anxiety for him and his family,' Rosamond said.

'He said that his previous insurer did not raise concerns when he informed them about fitting a tow bar. 

'This, combined with the fact that the modifications section of the purchase journey on MoneySupermarket did not list a tow bar, meant he had no reason to click 'yes' when asked about modification.'

Following a nine-month dispute with Flow - a subsidiary of Allianz - the Financial Ombudsman Service found in favour of the insurance company. 

However, the Financial Conduct Authority's Consumer Duty rules – which came into force in July 2023 – state that 'important information shouldn't be buried in lengthy terms and conditions'.

An Allianz spokesperson on behalf of Flow told This is Money: 'We understand the distress caused by this accident. Making modifications to your vehicle can have serious implications for your car insurance policy if they are not declared, and can lead to a policy being invalidated. 

'The policy chosen did not allow modifications and had we been informed that a tow bar had been fitted we would not have provided insurance. 

'The FOS has reviewed this case and its decision, which is binding, has found that the outcome we reached in this case was fair and reasonable.'

A MoneySupermarket spokesperson said: 'We’re confident that the supporting information we provide in our customer journey satisfies the FCA’s Consumer Duty requirements.'

However, Auto Express said it is not entirely convinced.

As such, the automotive magazine and website has written to the FCA requesting an investigation into the information regarding modifications on insurance websites. 

'We think the current wording typically shared on insurance sales websites around 'modifications' is a trap set for the unwary,' Rosamond added. 

'Insurance sales and comparison sites should offer greater clarity and detail on what constitutes a modification – especially in relation to tow bars, as we have seen – and provide specific information on the potential risks of getting a declaration wrong.

Auto Express also believes it is unreasonable for insurers, the FOS or FCA to expect an average customer to know that fitting a removable tow bar is the type of modification that could lead to a cancelled policy.

Rosamond continues: 'We also think that if an insurance company offers a policy it knows doesn't cover cars fitted with tow bars, then it has a responsibility to make that exception clear to potential customers before taking their money. 

'We'd like to think it would also ask potential customers whether their cars have tow bars fitted, before issuing policies at all.'

Allianz/Flow told Auto Express that it wouldn't be seeking to reclaim third party costs from the driver - even though it was entitled to do so following the Ombudsman's decision, but Rosamond wants the insurer to go further and cover the driver's costs.

Rosamond concludes: 'We told the insurer we hoped it would reinstate cover for the driver, as well as settling the third party claims in his case. 

'We also said we think Allianz/Flow does not appear to be acting in good faith, given the lack of clarity of information provided on tow bar fitment at the point of sale for its policies. Indeed, it looks to us as if Flow has jumped on a 'small print' infraction - one that has no bearing on the claim itself - simply in order to avoid a payout.

'We're waiting for responses but it is clear something needs to change so that no other drivers have to go through a similar ordeal. 

'Meanwhile, we urge all motorists to inform their insurers if their car has any modifications – however small they may seem, and whether they made them themselves, or it was a previous owner or even the supplying dealer – to avoid getting caught out in the same way.'