Insurers are using airline-style tactics to charge drivers extra for buying cover at the last minute.
Customers face paying hundreds of pounds more than if they had renewed early, a Money Mail investigation found.
Those who take out cover on the day it is due can be charged £200 more than they would have been 24 hours earlier.
In some cases, renewing late can see premiums doubled.
Firms are using computer algorithms to set the higher prices.
Last month, the Mail revealed that insurers had begun using information gleaned from customer data to charge more to drivers who bought a policy late in the evening, or who had shopping habits that supposedly indicated a higher risk of having an accident.
Now analysis of premiums offered to drivers shows that even those who shop around for a better deal on price comparison websites are being stung.
Insurers know when a customer’s cover is about to expire because they ask them to enter the date when they want their new policy to start on the firm’s website or on a comparison site.
Customers who call a company are routinely asked this question.
That means the insurer can tell whether someone is sensibly planning in advance or whether they are in a panic to renew their policy – and likely to accept a higher quote.
Customers face paying hundreds of pounds more than if they had renewed early, a Money Mail investigation found
Churchill and Esure are hiking premiums by hundreds of pounds for those who delay renewing their policies.
Typically, when a driver’s car insurance is due for renewal they will be sent a letter around a month before it expires.
Quotes used to be based on a driver’s age, experience behind the wheel, no claims bonus, where they live and the type of car they drive.
However, increasingly insurers are finding new ways to determine who they believe are the drivers most at risk of making a claim.
Analysis of figures based on millions of quotes over a three-month period by comparison site Comparethemarket found the cheapest day for renewing car insurance was 21 days before it is due – at a total cost of £481 for a typical driver.
However, every day costs more, hitting £540 a fortnight before the policy is due.
Eight days beforehand the annual price climbs to £605, £700 three days out, then £734, £795 – and finally £974 the day it is due.
Insurer Churchill charges a customer who buys cover 21 days in advance just £387. But if the same customer took out an insurance policy on the day it was due they would end up paying £612 – £225 more.
analysis of premiums offered to drivers shows that even those who shop around for a better deal on price comparison websites are being stung
And Esure would jack up premiums by £100 from £366 to £466 for the same customer, according to Go Compare.
LV= would offer a customer who booked their cover 21 days before renewal £405 but would hike this price to £570 for those who bought cover on the day.
Experts say that insurers use the point when customers buy cover as an indicator of risk – helping them to decide what to charge.
Those who delay buying until the day before their cover runs out might be viewed as disorganised or careless.
This could mean that they are more likely to have a crash or be too rushed to shop around for a better deal.
In a twist, those buying insurance extremely early may also be viewed as an indicator of an overly cautious or nervous driver.
Those who delay buying until the day before their cover runs out might be viewed as disorganised or careless
So anyone who renews their policy the moment they receive a renewal letter will pay a higher premium.
James Daley, founder of consumer website Fairer Finance, said: ‘We know that when we go on holiday we get better prices by booking at certain times.
‘But it seems unreasonable to use such budget airline pricing tactics on car insurance customers.
‘There urgently needs to be an investigation so the regulator can draw some boundaries about what is and isn’t acceptable.’
Dan Hutson, head of motor insurance at Comparethemarket, said: ‘People probably aren’t aware that they are being financially penalised for buying insurance at the last minute.’
A spokesman for the Association of British Insurers said: ‘Motorists should always make sure that they renew their motor insurance in good time, and not leave it to the last minute.
‘Some insurers may have data that links when you renew to the likelihood that you may make a claim.
‘Motor insurance is fiercely competitive – it pays to shop around to make sure you get the right deal for your needs, which may not always be the cheapest.’
A Churchill spokesman said: ‘The further a person is to their insurance start date when they obtain a quote, the less likely they are to claim.’
An LV spokesman said prices were calculated so that safer drivers did not subsidise riskier drivers through their premiums.
A More Th>n spokesman said: ‘Our data proves that drivers who obtain quotes on the same day their insurance expires, present a greater risk and this is reflected in their premium price.’
Esure did not comment.