The association's core activity is commercial product testing, recorded in its monthly magazine, Which? The magazine's circulation has dropped from 850,000 in 1988 to 683,000. This has caused a crisis of confidence, and morale was not improved by a strike over pay last June or by public criticism of Which?'s attempt to attract new subscribers with hard-sell mail shots.
The staff, who have been at odds with the retiring director, John Beishon, have welcomed Ms McKechnie's appointment. Her primary task will be to decide whether the association's definition of the consumer interest is too narrow. Advice about a new fridge or laptop is useful, but there are more pressing consumer concerns.
The most important of these are environmental damage to health; mendacious advertising; failures in the regulation of financial services and privatised utilities, in the effectiveness of the enforcement agencies and in the provision of health, housing, education and public transport.
Although she has not committed herself publicly, nobody familiar with Ms McKechnie's career or with her social outlook doubts that the Consumers' Association stands on the threshold of a revolution.
SHEILA McKECHNIE is a large, cheerful, emotionally uncomplicated Scot of 46 - a familiar presence, with her anglicised Lowlands accent, on the BBC's Question Time. She grew up in Falkirk, where she took maths, physics and chemistry as her sixth-form subjects at high school, and taught Sunday school. Her father, a baker, bequeathed to her a talent for shortbread, though she owes most of her considerable culinary skills to holidays in France with her longtime partner and stepdaughter.
At Edinburgh University she read history and, as secretary of the students' representative council, was drawn into the heady student politics of the late Sixties. "I felt incredibly liberated by leaving that sedate little Scottish town for the cosmopolitanism of Edinburgh," she recalls. "There was an enormous optimism and self-confidence compared with university life today. I had a sense of wonder, most of the time I was there, that this was happening to me."
The experience formed her character, and she never lost that optimism, though in the past 10 years there has been little reason for it.
Graduating with an upper second, she worked as a research assistant in labour relations, first at Warwick and then at Oxford, where she says she was radicalised by reading American feminist literature. She helped organise the National Women's Liberation Conferences at Manchester and Birmingham in the Seventies and was on the editorial board of Red Rag, a radical feminist periodical.
In 1972 the Wallpaper Workers' Union, worried by the aggressive recruiting tactics of Clive Jenkins's white-collar ASTMS, hired her as assistant secretary to organise supervisors, designers and other clerical staff in the industry. "Negotiating with companies like Crown and Sanderson's knocked some of the airy-fairy idealism out of me," she says. "I learnt that life is seldom clear-cut, and that there's usually right and wrong on both sides."
She spent two years teaching labour relations and women's studies at Manchester University, and had a regular slot on Granada TV's This is Your Right programme, answering questions about the Equal Pay Act.
Then, in 1974, Parliament passed the Health and Safety at Work Act. Although tens of thousands of employees were being injured every year by industrial accidents and degenerative diseases, few in the trade union movement understood the technical and medical complexities of the subject. Ms McKechnie took the trouble to instruct herself in it.
Clive Jenkins had been impressed by her competitive spirit at the wallpaper union. A significant number of his members worked in dangerous laboratories. Without much enthusiasm for the issue, he invited her to join ASTMS as national health and safety officer in 1976. He taught her how to handle the media, and left her to get on with the job. She made the union one of the most effective agencies in the country for the reform of life-threatening industrial practices, a model of enlightened trade unionism.
The housing charity Shelter was started in the Sixties by a Catholic priest, Eamonn Casey (since disgraced), and a Methodist minister, Bruce Kendrick, who were active among exploited private tenants in London's Notting Hill district. Des Wilson, whom they hired as its director, was the first person to recognise that it was not enough for a charity to lobby clandestinely in the corridors of Whitehall. If it was to achieve worthwhile changes in government policy it needed to enlist the mass media, particularly television, which had recently moved the nation with a play about homelessness, Cathy Come Home. Wilson transformed single-issue politics.
When Ms McKechnie became director, Shelter had lost its edge and direction. In common with other public-interest groups, it was being injured by left-wing elements that wished to use it as an engine of radicalism. The 1977 Homeless Persons Act, which introduced housing benefit, had been the greatest political achievement of the housing lobby, but many people would argue that Shelter's housing advice arm, SHAC, under Nick Raynsford, played a greater part in that than the parent organisation.
Recognising, like Sue Slipman at the National Council for One-Parent Families, that a lobby's strength lies in its independence from party interest and in the absolute objectivity of its research, Ms McKechnie fought a tough-minded internal battle to restore Shelter's effectiveness, widening its financial base and earning the respect of Whitehall and the media.
In his Campaigning Handbook, published last month, Mark Lattimer argues that single-issue campaigning has been more successful than mass-party politics. "The growth of a host of separate struggles has proved a more effective way of achieving social change than attempting to persuade different individuals to join together," he writes. "The harbinger of change is not so much a new dawn, more a thousand points of light . . . Perhaps the best analogy for campaigning now is not war, but surgery . . . The campaign strike should be as surgical as possible. Localised, precise . . . minimally invasive."
Ms McKechnie's experience at Shelter exposes the strength and weakness of this thesis. During her 10 years there, the Government continually cut its spending on public housing in the belief that a free market would provide a more flexible resource for a mobile workforce. It has been proved glaringly wrong, as the proliferation of inhabited cardboard boxes on our streets amply testifies. At the same time, the right-to-buy policy has reduced council tenancies from 6 to 4 million, diminishing the the number of citizens with a vested interest in public housing.
"The problem has been that the Government doesn't see housing as a social issue, but as a side-issue of economic policy," Ms McKechnie says. She and her team have campaigned successfully to limit the effects of a disastrous policy. One of the most valuable functions of a pressure group is the detailed monitoring of legislation. Her greatest victory has been to fight off an attack on the Homeless Persons Act in the Department of the Environment's green paper last February.
But she has not been able to halt the retreat from public housing. Nor has she been able to force the Government to restore housing benefit to 16- and 17-year-olds in order to get juveniles off the streets.
"There's a cyclical pattern to single-issue politics," says Raynsford, now a Labour MP and shadow housing minister. "Sheila transformed Shelter. It's a much stronger organisation, better placed to have an influence. But the world in which it operates haschanged. It's far harder these days to exercise that influence."
Unlike housing, which has not been central to Westminster politics since the Sixties, consumerism is politically hot. Failures in regulatory bodies and in the enforcement agencies have contributed to an impression of the Government's political weakness and administrative incompetence. Like Blucher at Waterloo, Ms McKechnie is a late arrival on the battlefield, but one to be reckoned with.