Marks & Spencer will not stock any brands that jar with environmental and ethical initiative Plan A, it pledged this week.

As M&S outlined a programme to become the world's most sustainable retailer by 2015, it said 50% of its own-brand product would carry at least one sustainable or ethical quality mark, with all converted by 2020. However, the retailer said the 350 fmcg brands it began rolling out to stores last year would not need to sign up to the initiative, although they had to still live up to the standards set by Plan A.

"This is more about our own supply chain and our farmers, but if any branded product jarred with Plan A then we wouldn't stock it. For example, we already said we would not sell cigarettes," said a spokesman.

By 2012, M&S said all its 10,000 farmers who supply meat, dairy, produce and flowers would be signed up to its sustainable agriculture programme, Farm for the Future. And by 2015, it would begin expanding the plan to the thousands of other farmers whose meat and produce is used as ingredients.

This next stage for Plan A would also make M&S the first major retailer to ensure that six key raw materials palm oil, soya, cocoa, beef, leather and coffee all came from sustainable sources, said chief executive Stuart Rose.