'The dome is not in danger of collapsing,' the Dean, the Very Rev Eric Evans, said. 'But the iron crampons which hold the stonework in place are rusting.'
Maxene Miller, of English Heritage, which has disbursed nearly pounds 16m of state aid to cathedrals over the past four years, said: 'St Paul's is certainly one of the more decrepit cathedrals because of the widespread use of iron clamps and pinning to hold the stonework together, which is now rusting and splitting the stone. It was built with very advanced techniques for its time.'
St Paul's introduced an entrance fee of pounds 2.50, and a further fee of pounds 2.50 for the galleries, three years ago. It is visited by 2.5 million tourists every year, and their contributions meet the cathedral's running costs. These, as in all cathedrals, are mostly salaries. The music alone in St Paul's costs up to pounds 500,000 a year.
However, the costs of repairing cathedral fabrics must be met by special appeals. In recent years, Salisbury has raised pounds 6m for its spire, and Worcester pounds 4m, though almost all the cathedrals of England have rolling programmes of restoration. These are slowed by a shortage of skilled labour as much as anything.
The Lord Mayor of London, Paul Newall, has made the St Paul's appeal his charitable cause for the year. Further funds are to be raised in the US by a New York businessman, William Miller.
The money will be spent on a programme of preventative work which will take 25 years to complete. The first 10 years' work has been scheduled. The registrar, Brigadier Robert Acworth, said: 'There is not a crisis now, but if we did nothing, there would be.'
Some of the problems at St Paul's are caused by its success. The feet of millions of visitors have worn down the stone floor of the nave by more than an inch, and air pollution has contributed to corrosion.