Comparison sites play a central role in helping households quickly shop around for the best insurance deals. But Which? Money has found quirks in their online forms that could inflate your home insurance premium by hundreds of pounds or invalidate the policy you end up buying.
While that sounds like more than enough information for insurers to generate an accurate quote, these forms still include compromises. Where detail is missing, insurers sometimes rely on assumptions and generalisations.
When cross-referencing questions between comparison sites and insurers we spotted differences in at least 30 areas, some of which could cost you.
Here, we explain what you need to look out for when buying your next home insurance policy to avoid being caught out.
We used five scenarios to test how much detail Compare the Market, Confused.com, GoCompare and MoneySuperMarket picked up and fed into insurers.
Here are three assumptions we uncovered that inflated premiums.
Declaring a flood in your property can affect how much you pay.
In our research, MoneySuperMarket and GoCompare only asked whether your home has ever been flooded, not when this happened.
We found that insurers interpreted this to mean that the flood happened in the last five to 10 years - yet the flood in our scenario occurred 20 years ago.
Some insurers will work on a worst-case scenario to ensure you are covered, but adding the extra detail could save you hundreds.
Impact on premium: the wrong assumption inflated the premium for one of our prospective policyholders by as much as £413.
Having a bankruptcy can also increase your home insurance quote by a significant amount.
In our scenario, the policyholder lived with a family member who had once been bankrupt.
Yet in the quotes we gathered via GoCompare and Compare The Market, we found incorrect assumptions at the insurer's end.
Based on the information provided by the comparison sites, some insurers assumed that the 20-year-old bankruptcy in our scenario hadn't been discharged, others that it was the policyholder's bankruptcy charge (rather than a family member's) or that the bankruptcy had occurred within the past five years.
Impact on premium: these incorrect assumptions cost us between 52p and £50 extra on the quotes we generated.
Your no-claims discount can help lower the cost of your home insurance premium.
Some insurers will acknowledge up to 10 or even 15 claims-free years.
However, all four comparison sites we looked at only allowed 'nine or more years' as the maximum you could declare.
Impact on premium: in our scenarios, this quirk made a slight difference of around £1.
While paying less for home insurance sounds like a win, it could leave you under-insured or with an invalid policy.
Here are three factors we uncovered that could artificially reduce your premium.
The amount of time you spend at home helps insurers determine the security of your property and possessions.
In one of our scenarios, one of the properties is not occupied at weekends.
MoneySuperMarket and Confused.com did not allow us to state this, yet they provided quotes from a handful of insurers that ask about weekend usage in their own questions.
Impact on premium: in this scenario, we were quoted a lower premium. The biggest difference was up to £98 less.
Home insurers are wary of large trees near a property, so they'll commonly check when you apply.
Yet we found that only three of the major comparison sites asked about this. GoCompare warned that you should check the insurers' assumptions, but didn't allow you to specify either way.
Impact on premium: we found confirming a tree's existence directly with the insurer increased premiums by up to £70.
The voluntary excess is the amount you would be happy to pay if you need to make a claim.
A higher voluntary excess usually makes quotes cheaper, while a lower one is likely to mean your quote will be more expensive.
When obtaining quotes we removed the voluntary excesses.
But this stipulation sometimes fell off our eventual quote, with three insurers applying an excess of up to £150.
This could later be lowered, but for those that think they've already made this clear, you could get a nasty surprise if you ever need to claim.
Here's what the four comparison sites said in response to our findings.
'At MoneySuperMarket we want to make it as easy as possible for customers to see a range of quotes and be able to switch and save on their home insurance.
'We work closely with insurers to ensure the information we ask for will enable them to provide customers with a complete quote based on their current circumstances.
'We also make updates to the customer experience based on the feedback we receive from people who have used our site to seek a home insurance quote.'
'We work very closely with our 70-plus home insurance partners to make sure we are asking our customers for the details needed to provide accurate quotes that meet customers' needs. By answering these, our customers should receive a selection of quotes to choose from that provide the appropriate cover at a price that fairly reflects the risk assessment made by the insurers.
'Before a customer completes their application they are shown a breakdown of the quote details as well as an IPID (insurance product information document) on the insurer's website. These show the details that the insurer has based its quote on, and provide details of the cover provided by the policy, plus any exclusions.
'It's imperative, whether someone has used a comparison website, a broker or gone direct to an insurer, that people read these documents carefully to make sure there aren't any mistakes. If there are any it's simple and free to amend the details at this stage.
'We continuously and proactively review and revise our services to reflect the needs of both our customers and our partners, and we will investigate the anomalies Which? has raised in detail to identify and correct any issues.
'We have very few customer service enquiries relating to price differences or issues with making policy amendments after leaving our site, but we treat any such feedback very seriously.'
'Our customer journey is designed to be as simple and accessible as possible for all, while recognising that every customer has a unique profile and need which will shape the quote that they are offered.
'When it comes to no-claims discount (NCD) on home insurance, insurers have cut-off points after which there is no further financial benefit; for many insurers this time frame is nine years.
'Different insurers have different risk models and, as such, factors which may influence the price of the quote - previous crimes and bankruptcies, for example - often vary between providers. It is therefore imperative for consumers to shop around when comparing policies. It is also advisable that customers who believe they have exceptional circumstances highlight this to their prospective insurance provider, as it could affect their premium.'
'We work closely with insurers to make sure our quote process is built to meet their requirements and provides accurate information based on their preferences. We then work together to proactively review this on a regular basis to make sure it is accurate and up to date.
'However, insurers can often update their process outside of this review, in which case we will make any changes required on a case-by-case basis.
'We also regularly review the questions we ask our customers to make sure they are able to provide the most accurate information and get the best price for them. We are committed to our customers and will always make sure we are able to offer them the best deals, and so we will always look to amend our question sets if anything is brought to our attention.
'Ultimately comparison websites are in the market to save customers time and money, and this is something that has been positively recognised by the Financial Conduct Authority.'
When shopping for home insurance use our simple steps to ensure you save time and money.
Compare direct: once you have identified the insurer that could offer you the cheapest quote through a comparison site, check the insurer's site directly for any differences or glaring errors.
Check the questions and answers: most insurers will let you check the questions your quote is based on. This is where you will find your pre-filled answers that have been fed through from the comparison site.
Call the insurer if you're confused: if you aren't sure what a question means or of anything else on your policy give the insurer a call.
Additional reporting by Dean Sobers