A row over wheelie bins could lead to Edinburgh being stripped of its World Heritage Site status, a Unesco official said yesterday.

Unesco's world heritage committee wants Historic Scotland to provide an impact study on the containers, which have been tested over the past 16 weeks in the Old and New Towns, in the latest chapter of the row that has followed their introduction.

Opponents, including two judges and eight residents' associations, are adamant that the original system using bin bags would be adequate if the bags were stronger, and that the bins are a blot on the streetscape.

Edinburgh City Council claims that the wheelie bins are cleaner, safer and more cost-effective. In April, the deployment of 89 caused heated clashes in the normally genteel New Town between residents and council officials.

New Town residents yesterday welcomed the world heritage committee decision. Gordon Coutts QC, a judge who lives in Heriot Row, said: ''We would absolutely welcome Unesco's intervention. That is what should have happened in the first place.

''Each and every one says they would prefer bags, albeit stronger ones. So far as the general tidiness of this street is concerned, there was no difference whatsoever.''

Susie Lynn, secretary of the Regent, Royal and Carlton Terraces Residents' Association, said: ''A great many of the residents are delighted the bins are going. People around here do feel that it upsets the character the place.''

Gaby Holden, secretary of the Drummond Civic Association, said: ''The black bags would be fine if they were collected earlier in the morning or were even a bit stronger. My fear is that some might be seduced by the convenience of not having to take out large black bags.''

The Unesco committee raised the issue at its last meeting in Suzhou in China in July. It was concerned enough about the situation to call for the study.

A Unesco source said: ''The world heritage committee will ask the UK government to prepare a report on the visual impact of the bins on the site.''

The source also said the committee has the power to remove world heritage site status and added: ''It is an option that can be used as a threat. Usually governments conform, and bins can be removed very easily. World heritage site status is a very prestigious label and most countries want to protect that.''

The council said it would make a decision on permanent deployment based on surveys and residents' responses.

A spokesman said: ''The trial has gone smoothly with no real operational difficulties, and the main issue remains one of the aesthetics of the containers.''

All 1143 properties involved in the trial have now reverted to their previous twice-per- week sack collections and the council will analyse comments and survey results.

Keep Scotland Beautiful has also carried out cleanliness surveys of the trials .

Edinburgh World Heritage Trust, made up of the former Old Town Renewal Trust and the New Town Conservation Committee, has carried out a survey of the sites. Council planning officers have also carried out detailed assessments.

Robert Cairns, the city environment convener, said: ''I am pleased at how smoothly these trials have gone and await the outcome of the consultation with interest. Once the results have been fully analysed, the council will consider what the best course of action is.''

The areas chosen for the trial site were Canongate, St Mary's Street, Cranston Street, Forth Street, Hart Street, Regent Terrace, Carlton Terrace, Royal Terrace, and Heriot Row to Fettes Row, bounded by Dundas Street and Howe Street.

A Historic Scotland spokesman said the request for an impact survey would be considered once it has been made.