More than half the appeals result in increased rents, and over the past five years rents assessed by the committees have risen by 14 per cent a year.
The Campaign for Fairer Fair Rents, a pressure group set up by angry tenants, advises tenants not to appeal.
The problem is most acute in London, where 82 per cent of appeals increased rents above those set by rent officers. One tenant ended up paying 26 per cent more.
The rent on Patricia Ledger's unfurnished and unmodernised Paddington flat was increased two years ago by pounds 400 a year. Last September it went up by more than pounds 4,000, from pounds 4,600 to pounds 8,800. The rent officer had assessed her rent at pounds 6,100, but the landlord asked for pounds 8,500 and appealed.
The committee then set the rent even higher than the landlord had asked for despite Shelter acting as advocate for Ms Ledger.
'We all think the system is iniquitous and Kafka-esque,' said Ms Ledger, an active member of the Campaign for Fairer Fair Rents. 'Most people are terrified to appeal because it is always weighted against them.
'The committees only take into account factors they want to hear. They don't take into account the 9,000 on the waiting list in Westminster or the 4,000 people homeless.'
If this was taken into account, she argues, committees would have to accept that market rents are inflated because of the continuing shortage of accommodation.
Another victim of the system is 93-year-old Kate Danziger, who lives on her own in a Kensington flat. Her annual rent has just gone up from pounds 5,300 to pounds 7,000. 'I'm not complaining,' she said. 'But it's a lot of money.'
Mrs Danziger is lucky because she can afford the new rent. 'I can't move, and I like it here,' she explained.
Many other elderly tenants, facing similar sharp increases after living in their homes for many years, have had to move.
As a tenant of a fair rented property, Mrs Danziger has a measure of protection from excessive rents. The rent officer, employed by her local authority, decided her fair rent should be pounds 6,450. The landlord appealed to the committee, which raised it to pounds 7,000.
Rents in a block of properties in Bayswater were increased by the rent officer from pounds 4,600 to pounds 6,100 but raised further by the committee to pounds 8,800.
Fair rents were established by the 1977 Rent Act but are being phased out as a result of the 1988 Housing Act.
Some tenants are still covered by fair rents - those whose rental agreements preceded 15 January 1989, when the 1988 Act came into effect, or who have moved but stayed with the same landlord or where people have become tenants after their leases ended.
In 1989 the average fair rent was pounds 1,321. In the third quarter of last year, for those decided by the committees, it was pounds 2,235 - a 69 per cent increase in a five-year period.
The committees comprise lawyers, surveyors and lay people appointed by the Lord Chancellor's department and the Department of the Environment. A spokesman for the latter said: 'We do not accept that professional members, who may have had experience of conveyancing or valuation in the residential lettings field, by virtue of that are generally biased against tenants.
'Candidates for membership of rent assessment panels are required to disclose their interest and experience of housing matters. Any significant activity as a landlord by the candidate or his or her immediate family would debar the candidate from membership.'
The spokesman said the high increases in rents agreed by the London rent assessment committees, and the high number of rent officer decisions overruled, were a result of administrative delays in 1991, which led to a backlog of cases.
He added: 'Fair rents in London remain considerably below those in the open market.' Average fair rents in the capital were pounds 2,451, compared with pounds 4,664 for those not controlled, he said.
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