A high-profile Scottish Government campaign to cut food waste had to be soft-pedalled to avoid offending the big supermarkets, a document leaked to the Sunday Herald reveals.

Campaign staff were forbidden from advising shoppers to buy less food or to ignore "buy one get one free" (Bogof) offers because Asda, Sainsbury's and Tesco were "extremely sensitive about this subject". Winning their co-operation for the campaign had been "very difficult", says an internal briefing.

Environmentalists have accused ministers of "selling out" to big business at the expense of pollution and waste. "You wonder which campaign will be neutered next in the supermarkets' Bogof deal with the Government," said Dr Richard Dixon, director of Friends Of The Earth Scotland.

The campaign, launched by Environment Minister Richard Lochhead MSP last October, included TV, radio and newspaper adverts, social media and a travelling supermarket roadshow. The aim was to try to prevent people throwing away up to one-fifth of their food, which is reckoned to cost Scotland £1 billion every year.

Over two months, teams were recruited to staff stalls at major branches of Asda, Sainsbury's and Tesco in Glasgow, Paisley, Falkirk, Edinburgh, Dundee, Aberdeen, Inverness and elsewhere. They were equipped with branded bodywarmers, baseball caps and iPads and told to "engage as many people as possible".

The strapline for the campaign was "shop smarter, waste less, save more". But, according to the official 69-page briefing for staff obtained by the Sunday Herald, they had to play down the central message for fear of upsetting the supermarkets.

After an outline of the key points to make on reducing food waste, the briefing gave staff a stern warning, highlighted in red: "Please note: the supermarkets are extremely sensitive about this subject.

"We cannot be seen to be telling people to buy less, not purchase Bogofs etc, when we are in Asda, Sainsbury's and Tesco. This was a very difficult partnership to secure due to the sensitivities so we must consider this."

The revelation has infuriated environmental groups, which regard tackling food waste as crucial. "The Government has sold out to the supermarkets just to get to give out a few leaflets in-store," said Dixon.

"The first thing to do to reduce waste is to stop buying so much stuff in the first place, but this has been the first thing thrown out the window to keep the supermarkets happy."

This was a "compromise too far", Dixon argued. "The big food retailers have pretended to support this campaign when the reality is that they are quite happy with the current situation where more waste by us means more profit for them."

Green MSP Alison Johnstone accused the Scottish Government of "kowtowing to the demands of self-interested supermarkets".

She said: "We will never tackle our over-consumption of food or the obesity crisis while retailers constantly push deals that encourage you to buy more than you intended."

The Scottish Government declined to comment directly on the leaked document, but defended its campaign to cut food waste. An independent evaluation suggested that more than 90% of those who visited the supermarket stalls took action to reduce food waste as a result, it said.

The partnerships with leading retailers were effective in reaching more shoppers, it argued. "The supermarkets have pledged to help households reduce food and drink waste," added a Government spokesman.

"The campaign addresses a number of actions that should be taken to prevent food waste such as planning meals, checking cupboards before you shop, and writing a list. Undertaking these pre-shopping habits means consumers are less likely to impulse-buy or stock up on more food than they need."

Sainsbury's said it was "very pleased" to have worked with the Scottish Government. "We are more focused than ever on providing ways for our customers to make their food go further and waste less," added a company spokeswoman.

Tesco and Asda referred queries to the Scottish Retail Consortium, which stressed that it was committed to helping households reduce food waste. Advice on storage, portion sizes and leftovers had helped reduce domestic food waste in the UK by 670,000 tonnes between 2005 and 2009, it said.

Head of policy David Martin pointed to evidence that there was only a "very small" link between giveaway promotions and food waste. "While just less than half the shoppers surveyed thought buying food on offer leads to a greater amount being thrown away, only 4% of customers reported throwing away more food when bought on special offer," he said.

"The main method of promotions in this area is cutting the price rather than Bogof offers, which are rare for fresh produce but one of a range of choices offering value to customers."