Lidl’s fashion prowess knows no bounds: ahead of Burns night on Sunday, the budget supermarket has started selling kilts. The viscose rayon mix skirt costs £29.99 and is part of a collection that includes a pleather sporran for £10 and a haggis for 99p.

Lidl first piloted the design ahead of last summer’s Commonwealth games. This “proto-kilt”, which was three yards shorter and £10 cheaper, sold out almost immediately. The new line has been rolled out in time for this weekend’s celebrations, and the collection is already close to being sold out in both London and Scotland.

But would a true Scotsman wear it? The kilt comes in at the requisite eight yards long, making it legit enough. It’s just the tartan that is causing a minor furore. The design – a muted, forgettable palette of greys, greens and blues – borrows freely from various, disparate tartans. Lidl claims it’s Highland Grey. According to the House of Tartan, it “resembles” Highland Granite. Brian Wilton of the Scottish Tartans Authority says: “It’s not a tartan I recognise”.

He would wear it … would you? Photograph: PR

There are no hard and fast rules when it comes to copyrighting a tartan, and most of the fashion houses mock up their own to avoid any copyright issues. There are around 11,000 registered and unregistered tartans knocking around, and about 120 new ones are created every year, so it’s nigh on impossible to keep tabs on every single design – it’s basically a free-for-all. Still there is a danger in these “pseudo” tartans “devaluing the genre” explains Wilton. “The problem is technology – there’s a lot of new software out there, which means anyone can design a tartan.”

There is an upside to the rise of the fakers. This renewed boom in tartan – over the past 12 months, the design has been a mainstay at Céline and Calvin Klein, and will be one of the key autumn/winter 2015 trends in menswear, thanks to Topman Design – is having “a demonstrable effect” on Scotland’s tourist industry, as well as the fashion world. Wilton helped design one used exclusively at Brooks Brothers which increased sales by £25m overseas. Why? “People in Asia love tartan.”

Wilton is loth to criticise Lidl too strongly – “it’s probably innocent enough” – and says, as a rule, if they see a rogue tartan design, they just suck it up or send a polite letter to the manufacturer. If an amateur designs a tartan for, say, their wedding? “We just grit our teeth. No one wants to hear their new baby is ugly.”