Completed in 1970, Northwick Park Hospital (above) was too late to be included in English Heritage's listing proposals, but it may be singled out next time. If so, it is bound to cause consternation. For the building is universally regarded as an ugly concrete sprawl, even though it has proved extremely adaptable.

Architect John Weeks remembers it as his most enjoyable project. 'The client was terrific.' The design was hugely influential but 'it was the wrong time for beautiful architecture', he admits. 'It was popular with users, but is wildly unpopular with everyone who looks at it.'

It was also unpopular with architects, who regarded the idea on which it was based - 'indeterminate architecture' - with horror. 'In their view it was the glove that fits all hands, and becomes none,' says Mr Weeks. At a meeting he attended at the Royal Institute of British Architects, 'indeterminacy was mentioned, and there was a distinct hiss in the hall'.

Nevertheless, in 1972, the Architects' Journal gave Northwick Park an upbeat review. 'This is a building in which it is obviously a pleasure to work and in which, at least, the business of being sick is not aggravated by tedium,' it asserted.

The Architectural Review was not so kind. 'In its half-built state it's not a very edifying spectacle - extinguishing any sense of park as it inexorably develops into an uncomfortably inchoate mass,' it wrote in 1970.

Long-time hospital staff member Sarah Turley's first impression of the building nearly put her off for good. Arriving for a job interview in 1985, she was presented with 'this concrete monstrosity' and couldn't find anywhere to park. She gave it up as a bad job. But a year later she was back and has worked there ever since, except for a 'miserable' period in the private sector when she used to see the hospital from the train and long to return, 'so it can't be that bad'.

She is now accident and emergency and medical assessment unit manager. 'The building doesn't do itself justice from the outside' and there is a lot of walking, she says. But the main hospital thoroughfare, a raised glass corridor, is good for networking. 'It's a progressive and very nice place to work and I've made lots of friends. Maybe it's because we all work in a concrete monstrosity.'