Off-licence chain Threshers is braced for an onslaught of bargain-hunting drinkers as an online discount voucher is downloaded by millions of people.
The voucher was intended for suppliers and friends only
The 40%-off wine and champagne voucher was intended for suppliers and their friends, but has been distributed widely via blogs, email and chatrooms.
Queues have formed at one store while the Threshers website has crashed under the strain of demand for the offer.
"It was never intended to get this big," a company spokesperson said.
The company admits it is slightly concerned about the popularity of the offer.
"We are waiting with bated breath... Early next week, we should get the figures for what level of business we have seen this week and over the weekend," the spokesperson added.
"This is a better offer than normal and it could end up hitting our profit margins."
The 40% discount voucher applies to wine and champagne purchases at stores in the Threshers, Wine Rack, Bottoms Up, Haddows and The Local chains and runs until 10 December - although the small print suggests that it applies only to orders up to £500.
'Power of the web'
It first appeared on the website of South African wine company Stormhoek, which estimates that it has been downloaded more than 800,000 times.
"What has taken us by surprise is the scale of consumers talking to each other and passing it on to the next person," said Stormhoek's Alistair Pearson.
"I think the company are now a little bit worried that they will be able to handle the level of trade, but they have over 2,500 stores and know this business."
Queues have formed at some stores
Despite the size of the discount, he still expected that Threshers would make a profit on the offer.
Robert Dirskovski, head of interactive media at the Direct Marketing Association, told the BBC that the Threshers case demonstrated the power of the web.
"It lends itself perfectly to passing things on to your friends and relatives - it is what we call viral marketing.
He said that viral marketing was a useful tool for companies, especially as UK legislation prohibits unsolicited commercial emails to people that have not already made purchases or inquired about them.
"It is a very good way of collecting data. Once you have availed yourself of the offer, a retailer can then send you e-mails."
Retail experts say a number of High Street chains have begun using this tactic in so-called "secret sales".
Oasis, New Look, Selfridges, Gap, Borders and Habitat are reported to have employed the tactic.