GardX’s Coutin added: “If a dealer is selling at £199 we say that’s not enough – you can achieve £299 and up to £500 for prestige cars.”

Paintseal, whose Gen-3 Glasscoat is endorsed by groups like HR Owen, Snows and Gordon Lamb, said its pack, costing from £30 to £70, should return the same sort of margin as rivals, although Collins acknowledges that the cost to the customer in many cases is around £180.

Collins responds to consumer comments on motoring websites that the cost seems excessive and the benefits questionable by saying: “The public has been misled into believing that they can treat cars themselves with off-the-shelf products and then complain about the result. It’s critical that prepping is carried out thoroughly by trained valeters and this, combined with the time needed to apply the treatment, is obviously a dealer overhead. We’re aware of adverse comment and recognise the need to be much proactive.”  

Paintseal’s modular sales support features a five-step-to-sale, with the company about to offer an online option.

For Essex Auto Group, Diamondbrite has been the product of choice for the past three years, following a change of supplier. Keith Janes, general manager at the company’s Dunton site, said: “Sales support is very good, with weekly visits to check on supplies and monthly reports on penetration levels within the group, presented in a league table.”

Janes said product credibility is dependent on strict adherence to standards. “It’s been known – not within our group, I hasten to add – to ‘stretch’ a one-pack product to two cars.”

He described paint and fabric protection as “a lifestyle choice, whether someone enjoys cleaning the car”. Its undeniable attraction was an improvement in the vehicle’s appearance that could enhance trade-in value.

Janes said that, depending on pack options, he looked for a net margin of around £180.

“In the past, there was always better penetration on new cars, with customers reasoning that they wanted protection from the outset.

“But now we’re seeing sales for used cars at more or less an equal level–up by 20% over the past three to four years.” He added that penetration was across-the-board, irrespective of the car’s sticker price. Diamondbrite’s other customers include Ford Retail, Vertu, the Retail Automotive Alliance and Jardine Motors.

Thame Service Station, which sells around 1,000 used cars a year, has been a customer of Autoglym’s LifeShine treatment since the beginning of 2012.