The most affluent classic car collectors typically duke it out in auction rooms to get their hands on the rarest, most exclusive and desired models from past eras.

Aston Martin, Bugatti, Bentley, Ferrari, Jaguar, Lamborghini, Porsche, Rolls-Royce: just some of the names that traditionally command most attention - and highest bids - from the wealthiest petrolheads looking to add cherished motors to their garages.

But when it comes to the cars posting the biggest spike in value in recent years, one mainstream brand is putting its lavish counterparts to shame - Ford.

High performance 'Fast Fords' from the seventies through to the nineties era have become serious collector's items of late - and none more so than the Sierra RS Cosworth.

The souped-up eighties family car cost up to £19,950 in showrooms four decades ago. That's around £59,500 in today's money with inflation factored in. 

But wind the clock forward to present day and well-heeled enthusiasts are willing to splash six-figure sums on the best surviving examples.

Later this month, six Sierra Cosworths will go under the hammer at an auction in Northamptonshire. Collectively, they are predicted to sell for an eye-watering £1million. 

Which begs the question: how has the market reached a situation where an eighties hot hatch is worth the same as - if not more than - a Jaguar E-Type?

The Sierras heading to the block on Friday 24 and Saturday 25 July comprise a varied - but highly valuable - selection of the nameplate.

Arguably the ones that will cause the most frenzied bidding are three of the limited-run RS500 Cosworths of which only - yes, you guessed it - 500 were produced over a four-month period between March and July 1987. 

The most valuable of all is one of the last examples; number 468 - registration E84 CDB - which is one of only 56 that were officially painted white.

The vast majority - 392 cars - were black, while the rarest colour of all is Moonstone Blue, of which only 52 left the assembly line.

The car has covered just over 16,700 miles from new, making it one of the least used examples still in existence.

It formed part of the BonkeRS Collection - widely regarded as the best-known private collection of significant Ford RS models in recent years.

It too appeared in Dan Williamson's 2016 book Factory Original Ford RS Cosworths as a 'benchmark example of originality'.

Iconic Auctioneers, which hosts the sale at the Silverstone race circuit at the end of the month, believes it will trigger bids in the region of £150,000 to £200,000.

A second example - registration E454 EFV, finished in black and number 195 of 500 - is another motor from the BonkeRS Collection.

It is supported by long-term early ownership, RS500 Register confirmation, original factory literature and service history that covers its 44,599 miles to date.

The guide price is £80,000 to £100,000. 

And completing the trio is the most exclusive colour of all - a blue RS500, number 470 of the output with the registration E111 UD9.

It too has been retained in long-term ownership and is almost completely original, despite clocking 67,260 miles over the last 40 years.

The estimate is £90,000 to £120,000.

A competition RS500 from the famous Group A racing series which contended both the Australian and British Touring Car Championships is also being offered to the highest bidder with a guide price of between £400,000 and £450,000.

Also offered is a non-RS500 1987 Ford Sierra RS Cosworth in Diamond White - registration D404 BAB - which boasts single-family ownership, just 6,242 miles from new and a remarkable level of originality. 

First registered in 1987, the three-door Cosworth spent its first 37 years with its original owner before passing to his son. 

It was placed into private garage storage in 1988, still displaying its 1988 tax disc today. 

Briefly recommissioned in 2015 and again in 2025, it has only undergone 'sympathetic maintenance' since.

Its incredible originality and time-warp condition means it could eclipse some of the rarer RS500 examples with an estimate of £100,000 to £120,000.

The last of the six Sierra models is a 1991 Sapphire Cosworth Rouse Sport 304-R - registration J88 COS - which is one of the unicorn road-going Sapphire Cosworth conversions by racer and tuner Andy Rouse.

Rouse built the car for his race team's doctor - Dr Roger Melhuish - and it has been kept in his garage since new.

Adding to its desirability, it is believed to be one of only two surviving Diamond White 4x4 examples currently registered in the UK, and bidding is expected to exceed £50,000.

Commenting on the availability of the collection of 'Cossies', Rob Hubbard, auctioneer at Iconic Auctioneers, said: 'Performance Fords continue to command huge affection and serious collector interest, and this group of Sierras is a wonderful reminder of why. 

'From highly original road cars to a Group A racer with period touring car history, these are cars that speak to enthusiasts at every level.'

Ford Sierra Cosworth: A brief background

The original Ford Sierra RS Cosworth was the first Ford to wear the Cosworth badge and was presented to the public at the Geneva Motor Show in March 1985.

It was introduced as a means of homologating the Sierra for Group A Touring Car racing, with a requirement that 5,000 cars were built and sold before the competition version could hit the track.

Launched for sale in July 1986 and based on the three-door Sierra body-shell, it was designed by Ford's Special Vehicle Engineering (SVE) and was powered by a Cosworth-designed 2.0-litre turbo engine of now-legendary repute. 

At the time, the Sierra Cosworth was a new kind of performance car - a 'blue-collar hero' able to humble true sports cars.

The RS500 was announced in July 1987 and had a mechanically uprated Cosworth engine (more like the one to be used in competition), with power boosted to 224bhp, modified bodywork and the cachet of being hand-assembled.

That makes the RS500 the ultimate 1980s Fast Ford in the eyes of enthusiasts and classic car collectors.

In total 5,545 cars were built, of which 500 were sent to Aston Martin Tickford for conversion to the Sierra 'RS500 Cosworth'.

If the RS Cosworth was a homologation car, the RS500 was an evolution special.

Once Ford had built the requisite 5,000 RS Cosworths, Group A rules allowed an upgraded 'evolution' model to be launched. 

This could carry changes focused on improving its racing potential, provided Ford sold 10 per cent of the original number as road cars, hence its 500 nameplate. 

The eye-watering prices being paid today 

The value of the RS Cosworth - particularly RS500 examples - had been climbing significantly through the 2010s and early 2020s.

But in 2022, prices really took off. 

Iconic Auctioneers - formerly Silverstone Auctions - sold a 'standard' Sierra RS Cosworth for a staggering £132,750 in November that year.

Completely original and with fewer than 9,000 miles on the clock, the winning bid for the car was £10,000 over the previous record.

But it was the February 2023 sale of registration E378 TKN that really inflated the cost of these cars.

The 5,192-mile example of the sought-after RS500 sold for £596,250 - 30 times its 1980s original showroom price, and over four times the previous record set only three months earlier. 

The auction house described it as 'perhaps the finest example of the rare Sierra Cosworth RS500 to survive today'.

In an expert column written exclusively for Daily Mail and This is Money, classic car valuation expert John Mayhead described the 2023 sale as an 'outlier' that might never be repeated.

However, it's clear that the price paid three years ago has pushed the general value of these vehicles higher than ever.

'The RS500 was the ultimate homologation Ford Sierra, and it is rightly prized by collectors,' John explains. 

'Prices peaked thanks to a one-off huge sale in February 2023 of a low-mileage car by Iconic Auctioneers that netted nearly £600,000 but that price hasn’t been nearly reached in recent years for anything other than full racing cars with good history. 

'The gap between fair examples and the most original and pristine, 'concours' examples has grown significantly over the last decade though, as collectors scrap for the very best examples.'

While far from the £596,250 record, in the last two years, Iconic Auctioneers has sold two RS500 examples for over £100,000.

To put that into perspective, the average sale price of a sixties Series 1 Jaguar E-Type typically ranges from £70,000 to £150,000 today.