The average quote for annual comprehensive car insurance has fallen to £594.86 – a 9.8% fall from the figure of £659.53 in July last year, according to AA Insurance.
This is the biggest decrease since the AA insurance index began in 1994.
The figure for third party, fire and theft insurance has also dipped in the last 12 months, going down 4.8% to £820.58.
Comparing July 2013 figures with those of April, the AA showed that comprehensive insurance has fallen 3% and third-party insurance is down 2.2%.
Over the last 12 months, car insurance costs have fallen for all age groups, with those aged 23 to 29 enjoying the biggest decreases with their average costs dipping 12.8% to £738.93.
All age groups have seen 12-month falls of at least 5.4% except those aged 70 or above who have had to settle for a 3.9% fall in premiums. On average, those aged 60 to 69 have the cheapest annual insurance (£342.73) and those aged 17 to 22 have the most expensive (£1,210.54).
AA Insurance director Simon Douglas said: “This will be welcome news for hard-pressed motorists facing sharp fuel price increases.
“Insurers were facing a fast-widening gap between premium income and claims costs, largely driven by whiplash injury claims and fraud which saw very sharp premium increases between 2009 and 2011.”
He went on: “That gap is closing and premiums are falling again thanks to competition, as well as improved fraud detection by the insurance industry and tightening of the law that is beginning to curb the number of spurious new whiplash injury claims.
“The news that hundreds of rogue ‘no-win no-fee’ claims firms have been reined in is welcome and in part, falling insurance premiums reflect that.
“I hope that Britain’s shameful reputation as being the ‘whiplash claim capital of Europe’ will now be put behind us.”