Read Ruth Gledhill's blog on the appeal

Westminster Cathedral, the UK's flagship Roman Catholic place of worship, could be forced to close within a decade if cash is not found for urgent repairs, clergy warned today.

Parts of the Byzantine-style building, which opened in 1903 but has never been completed, are now in danger of structural collapse if urgent repairs are not made.

Launching an appeal for £3 million, the Archbishop of Westminster, Cardinal Cormac Murphy-O'Connor, said: “Westminster Cathedral has been a symbol of the Catholic presence at the heart of our nation for over a hundred years. It is a Grade I listed building that is recognised as one of the finest examples of Victorian architecture and Byzantine art in the world. However, time has taken its toll and we must now take urgent action to ensure the future of this living house of prayer.”

The cathedral, which unlike many of its leading Church of England counterparts has no admission fee and depends entirely on voluntary donations to meet its running costs, is in danger because of serious deterioration in three of its four domes and their supporting brick arches.

Work to repair them must begin almost immediately, and the building's electrical and mechanical systems also need modernising. The work will also allow the Church to reopen the high-level galleries which were closed more than 30 years ago on health and safety grounds.

Mass is celebrated 41 times a week at the cathedral and 4,000 worshippers pass through its doors each Sunday. It is a regular haunt of new Catholic convert Tony Blair.

Monsignor Mark Langham, administrator, said it was still hoped to complete unfinished areas, such as mosaic work, but this was more urgent. He said the appeal arose because serious structural problems were discovered in the course of routine maintenance. "We need to deal with it immediately otherwise we won't have anything to put mosaics on.

"It is not at the stage where we have to close the cathedral now but our maintenance staff estimate that in five or ten years time, if we do not do anything now, we will be in trouble. We will have people coming round saying it is dangerous and that no-one can come in. This is the time to take action, to ensure that the building is kept safe."

He said some individuals had already promised cash, and there had even been some donations from members of the public who became aware of the appeal within hours of its launch and a banner going up outside the main doors reading: "Westminster Cathedral is in urgent need of your help."

Father Mark continued: "Yes, the Lord will provide but we certainly believe he works through humans as well. He wants to meet us half way. We've got to buy that lottery ticket before He'll allow us to win."

Patrons of the restoration appeal include actress Patricia Routledge and the historian Sir Roy Strong.

Twentieth-century “firsts” at the cathedral include Sir Edward Elgar conducting the first London performance of his setting of The Dream Of Gerontius in 1903 and a visit by US President John F Kennedy in 1961 for the baptism of his niece.

The cathedral features in the 1940 Hitchcock film Foreign Correspondent with a would-be assassin falling to his death from the bell tower. Hitchcock, who died in 1980, also asked that his own Requiem Mass should be held there.

The first Mass celebrated in the UK by Pope John Paul II during his visit to Britain in 1982 was in the cathedral.

The Queen also visited in 1995 to mark the centenary of the cathedral’s foundation, the first reigning monarch to attend a Catholic service in several hundred years.