Anyone who tries buying a flat quickly learns why the term caveat emptor was coined. Because most flats are leasehold, buyers have to take into account the fact that the lease will eventually run out, service and maintenance charges are often exorbitant, and relations with neighbours, who may live directly above or below you, have a tendency to be more-than- usually tense.
There is an additional problem, however, and it relates particularly to recently converted flats. In the 1970s and 1980s, the rise in property prices, combined with an increasing demand for accommodation for single and divorced people, meant that thousands of large Victorian houses were turned into flats and bedsits. In the mania to convert, many house-owners and property developers didn't bother seeking planning permission.
I discovered this to my cost when I bought, and later sold, a flat in Shepherds Bush, west London. A local authority search revealed that planning permission had never been sought to turn the three-storey house into apartments. Not surprisingly, building societies generally refuse to give loans on properties converted without permission.
Luckily, the Town and Country Planning Act 1990 provides a handy loophole that says if a converted property has been in its new use for more than 10 years without anyone complaining, the need for planning permission becomes invalid.
It seems like an odd situation - a way of allowing people to get away with breaking the law if they break it for long enough. "The planning system tends to be reactive," says Michael Haslam, who chairs the professional activities committee of the Royal Town Planning Institute.
"And if people do things and get away with it without anyone complaining, then perhaps there isn't a problem." Haslam acknowledges, however, that conversions on a large scale bring wider issues: "If a house is in an area of predominantly single families, for example, it changes the character of the area. This is one reason why the Government is seeking to bring in controls over houses in multiple occupation."
When I bought my flat in 1994, I was lucky, or so I thought, that my building society was happy to accept as proof a local authority ratings slip that showed the house had been in use as flats for more than 20 years. It was when I sold my flat earlier this year that the problems started.
For most mortgage lenders, definite proof that a flat or other property has been in use in its current form has to come from the local authority, in the form of a Certificate of Lawful Use and Development.
The certificate currently costs pounds 190 (prices are fixed nationally) and the authority will demand concrete evidence from the owner of the property's usage. Once the application, with suitable evidence, has been received, the authority is obliged to give a yes or no answer within eight weeks.
It sounds reasonable in theory - but in practice, it can be a frustrating process. When it came to selling my flat, I was on the verge of exchanging contracts when the buyer's building society suddenly announced it would not give my buyer a loan without a certificate. The certificate was applied for - but it was another 11 weeks before it was received.
The delay arose because the authority decided - after three weeks - that the evidence my solicitor had presented (the authority's own council tax records and the old ratings slip) wasn't adequate and it needed to see more. Fortunately, my buyer was willing to hang on.
The issue doesn't just affect conversions, however. Anyone buying a property that has had additional building work, such as an extension or the addition of a conservatory, needs to ask questions about planning permission.
In the case of building work being undertaken, the rule is that if no complaint has been made after four years (rather than 10 years, as in the case of changed usage), a certificate can be applied for. But why do so many people make alterations without seeking permission? "Ignorance is part of it," says Haslam. "That is no defence in law, but the planning system is quite complicated and the average citizen never comes into contact with it."
Haslam warns that buyers should always be wary about planning permission - particularly so, he says, if they are buying outright: "I've seen over the years many people who have bought properties for cash, then had problems when they come to sell that they wouldn't have had if a building society surveyor had had a look."
For more information, call the Department of the Environment, Transport and the Regions on 0171-890 3000 for the leaflet `Lawful Development Legislation: A User's Guide'