People moving into new-build properties can't get vital cover for their home or car because insurers don't recognise their postcodes.
Out-of-date databases held by many insurers prevent them from offering cover for car or home contents to customers who have moved, or are moving, into brand new flats or houses.
It means those who rely on their car have been left in the lurch unable to drive without cover, while others have found they can’t insure their new home - in some cases making it difficult to validate mortgages.
Check out our guide for the best car insurance and home insurance quotes around.
How have people been affected?
We've heard from frustrated consumers who have been left unable to take out a new policy, renew an existing one, or even change the address on an existing policy to that of their new-build home.
Charlotte from Hull told us how she'd been left high and dry when her former insurer Hastings cancelled her car insurance policy following a move to a new-build home.
She said: "I rang to change my address on the policy due to a house move but was told that it couldn't be found - even though it's registered with Royal Mail and I've been getting post from other companies.
"I've now got a car at my new address without valid insurance and face having to shell out extra for a new policy."
Her story is far from an isolated case, with scores of disgruntled customers of various insurance companies taking to Twitter over recent months to vent their frustration about issues registering a policy with a new build address.
@AvivaUK as a loyal customer I'm fed up you guys couldn't offer me insurance for my new build I move into in February #LosingMarketShare— Tom Hennell (@THennell) November 5, 2016
Changed my car insurance to my new house...and they cancelled my policy as they can't cover me because it's a new build! 😳 #balls— Kirsty Paterson (@PatersonKirsty) September 12, 2016
So I can't insure my house as it's a new build and not showing on your system, well done @MORETHAN. Trust me it is real!
— andy burgon (@andy2484) August 19, 2016
@HastingsDirect your company is useless cancel my car insurance because I got a new build.
— Chris Pomeroy (@ChrisP77366871) June 20, 2016
Fuming @RAC_Breakdown RAC insurance just cancelled my car insurance on spot coz their system didn't recognise my new build postcode #inept— Terry Whalley (@TerryWhalley) March 3, 2016
What's causing the problem?
The issue appears to stem from big administrative delays getting new postcodes generated by the Royal Mail onto insurers' databases.
When a developer or house builder erects a property, it must first contact the relevant local authority's planning and building department near completion in order to get an officially recognised address.
This usually involves correspondence to the council's 'street naming and numbering' officer who then decides on an address including postcode - and registers it with the Royal Mail's Address Development Centre.
The new postcode won't go 'live' until staff at the Royal Mail centre are informed that mail can now be delivered to the new address - a process usually triggered by a phone call from the new property owner, developer or house builder.
Once this authority is given - and it usually takes just 24 hours - any company can then find the new postcode on the Royal Mail's postcode address file.
However, while the postcode may be live, there's no guarantee a company - whether an insurer, bank, utility firm, etc. - will have it on their database. Whether a new address is there or not will depend on how often the firm updates its databases; and this can vary from daily to weekly or even monthly.
It's up to each individual firm - in this case, insurance companies - to decide how often they refresh their database; and the cost of different types of update can be a factor, with higher charges for more regular updates.
If an insurer only refreshes its database monthly, it can leave people who have moved to a new-build in the lurch until the update comes through.
"The problem is that postcode info is being fed through to the Royal Mail but it's not reaching insurers quickly enough," one industry insider told us. "And with the rate at which new properties are being built, this is clearly a major concern."
Is there a way around this?
If you're moving into a new-build property, your best bet to keep your insurance in order is to stay on top of the postcode application process.
As soon as you know your offer's been accepted for a new-build, get in touch with Royal Mail on 0345 774 0740 or visit its dedicated online service as soon as possible to start the process of registering your new address. If your insurer only updates its database every month, you'll at least give it much more time to get the postcode onto its files.
Another tactic, which may work if you're drawing a blank online, is to try calling your insurance company directly to speak to a call centre and providing them with full details of your particular case.
A spokesperson for Direct Line said: "In the event that we have the postcode on our system but do not have the exact address, our customer service agents are able to manually enter the address and provide a quotation for the policy.
"However, if we don't have the postcode for the property on our system, we are unable to assess the risk and therefore unable to provide a quotation."
What does the insurance industry say?
A spokesperson for the Association of British Insurers said: "Insurers will be aware that, on occasions, there may be delays in the full address being registered but will want to be able to assess the risk and quote for as many new builds wherever possible.
"Anyone moving to a new build house should get in touch with the building company/developer and Royal Mail as early as possible to ensure the address is registered."
We also asked the insurers for a response to consumers' difficulties.
A spokesman for More Th>n said: "New builds are updated on our systems quarterly when this information is provided to us by an external supplier.
"Whilst rare, we recognise the frustration a homeowner moving into a new home may encounter in trying to get an online quote for a home or even their car that our computer system may not yet recognise. We would ask that customers call us so that we can make arrangements to provide them with a competitive quote."
A spokesperson for Aviva said: "To ensure we send policy documents to the correct address, we need to wait for the address registration process with Royal Mail to have been completed, which can sometimes take a little time.
"We would advise those moving to a new build house to get in touch with the building company/developer and Royal Mail as early as possible to ensure the address is registered as soon as possible.
"To check whether the address has been recognised by insurers, it might be worth consumers checking to see how many providers have their address available or sharing experiences with neighbours and the builders to check which insurers are available."
A spokesperson for Hastings said the problems with Charlotte's policy had been resolved but didn't want to comment further. An RAC spokesperson also said the company was unable to make a comment.