Just days before the Office of Fair Trading publishes its report into 'bait advertising' and other potentially misleading pricing practices, Marks & Spencer has denied allegations that a £10 Champagne deal contravenes the rules.

In TV commercials aired on ITV, Channel 4, Five and cable channels shown between Wednesday and Friday last week, M&S advertised that its own-label Louis Chaurey Champagne was reduced from £30 to £10, with the deal starting on Thursday.

But customers were quick to complain on online forums that their local store had sold out, even when they visited at 9am on Thursday. Some stores had "sold out more tomorrow" signs prepared but immediately sold out the following day, too, ­according to reports.

"Lol what a con....sold out at 9:45 in Edinburgh...probably had 20 bottles. M&S know how to do it!!" wrote one. "Sold out in Barrow too (09:00). Pity, I was after a couple of bottles for Xmas. Think staff must have got it all as I was there as the shop opened," posted another member of the HotUKDeals forum.

Next week the OFT will unveil the findings of its year-long study into the ­advertising of prices. The report is set to reveal how fair trading rules will apply to pricing practices common in supermarkets such as bogof deals, and how the regulator will pursue retailers who fall foul of the line.

Among practices banned by consumer protection rules is bait pricing advertising an offer where availability is limited and there is little chance customer expectations will be met.

The OFT is likely to say next week that simply stating "hurry while stocks last" may not be sufficient if availability is severely restricted. In its draft proposals, published in August, it also said retailers should draw attention to the volume available if they have less than 50% of anticipated demand.

M&S said it had ordered 1,000 times more bottles of the Champagne than it had sold in the whole of the previous week. "All our stores had extra supplies of Louis Chaurey Champagne for the promotion," said a spokeswoman. "Our £10 Champagne deal was extremely popular. We bought our single-biggest order of Champagne for the promotion. However, a small number of stores sold out quickly.

"We take every measure to ensure that we comply with legal regulations and advertising guidelines and would strongly refute any claims that this was bait advertising."

IPM head of insight Colin Harper said: "It's interesting that 1,000 times normal order volume hasn't been enough to satisfy the shopper. It proves promotions are more powerful than even retailers and manufacturers believe. Managing them better has to be the priority next year."