The committee commissioned by the Arts Council to look into opera and ballet provision in London, which reported last week, said there was "an obvious need to stagger closure of the two main houses".
A Royal Opera House spokesman said yesterday that there were urgent safety reasons behind the redevelopment.
At the Coliseum, home of the English National Opera, a spokeswoman said: "The issue of the overlap is a bit tricky but if we were to wait we would be into the next century before we could make the changes necessary for a more efficient repertory and better public space."
The Arts Council is to rule on the report produced by a committee under the chairmanship of Dennis Stevenson, a businessman and chairman of the Tate Gallery, by the end of March. The report has shocked Britain's dance community in ruling out any prospectof a national dance house in favour of a "dance house network" of venues which would include the Coliseum, Sadler's Wells and numerous other smaller spaces throughout the country.
Christopher Booth, artistic director of Ballet Rambert, and a leading member of the campaign group Dance UK, said: "No answer other than a national dance house will satisfy the whole dance community. The problem with a group of buildings is that we don'thave control over those buildings. They are run by opera companies.
"The Coliseum is large with good sightlines but charges a dance company £75,000 a week rent. The Saddler's Wells with about 1,400 seats is not large enough for the big companies.
"Dance continually suffers from being the poor relation to opera and other art forms. We need our own building on London's South Bank with one large space which can be sub-divided for middle-scale companies, and a smaller theatre for the small companies."
Val Bourne, artistic director of the award-winning Dance Umbrella group of contemporary companies, said: "I accept we couldn't fill a national dance house every night all year round. Music and opera could take place there too on a visiting basis. But dance would at last have priority."
Many in the arts establishment were shocked that both opera houses plan to close at the same time.
Although both hope to use alternative venues such as the Lyceum or the Theatre Royal Drury Lane, there is as yet no guarantee that either will be available.
Val Bourne said that few of the dance companies that use the Coliseum had realised about the closure, and added that it did not seem to make any sense to be without both venues.
Leading article, page 14Reuse content