Blue plaques were thought up by the Royal Society of Arts, which placed its first in 1867 at the birthplace of Lord Byron in Holles Street (sadly, since demolished). The RSA was clearly cautious about who exactly deserved recognition: by 1901, when the London County Council took over the scheme, it had put up only 36. Responsibility transferred to the Greater London Council in 1965, by which time there were 262. The GLC's own abolition led to a plaque at County Hall celebrating the "Home of London Government from 1922 to 1986" and to English Heritage picking up the baton. In the 12 years since then, English Heritage has raised the number to nearly 700. And with its new plan, the scheme will become a national phenomenon.
A flick through the Blue Plaque Guide reveals the eclectic nature of those remembered - artists, poets, clowns, cricketers, empire builders, wigmakers, royal concubines, socialists and socialites. It is revealing too about the transient nature of property and the uses to which it is put: the poet Alexander Pope's plaque is on a pub in Chiswick, while the music hall entertainer Bud Flanagan lords it over Rosa's Cafe in Spitalfields.
Guiseppe Difruscia, the owner of Rosa's Cafe, was surprised when English Heritage approached him about putting up the plaque, which marks the spot where the leader of the Crazy Gang was born. "I had no idea about it before they got in touch. I didn't know of him - I was only about 10 when he died," he says. The plaque, which went up in 1996, has had no effect on his business, according to Difruscia, but it has received a lot of attention and led to some interesting encounters: "I had a lady in this morning whose mother was once engaged to Bud Flanagan and she brought me in some of his records. I do get some nosy people coming in as well, but mostly it's nice. It isn't a nuisance because I'm used to chatting to people."
At the other end of town - and the social spectrum - is the plaque to Sir Christopher Wren on the house near Hampton Court at East Molesey in Surrey, where he lived for the last 20 years of his life. The house is now home to former Tory MP Toby Jessel, who has lived there since 1969 and sugges- ted the idea of the plaque to English Heritage.
"A lot of people are astonished that there wasn't a plaque to Christopher Wren before 1996, but the thing was that I was a member of the GLC and didn't feel it was right to ask them to put one up. I didn't get round to suggesting it to English Heritage until 1990 and their processes are very slow. There was no queue-jumping, even for Christopher Wren," he says.
Jessel is a committed Wren-enthusiast and very proud of his association with the great architect. "I'm delighted with the plaque. It gets seen by a great many tourists and visitors. Not a day goes by without a crowd of people looking at it," he says. His pride even extends to a spot of maintenance: "I wipe it with a damp cloth about once a month - it's on a very main road and that stirs up a lot of dust, so it needs wiping regularly."
Apart from needing the occasional polish, the blue plaques are remarkably sturdy objects - the earliest survivors date from 1875, commemorating the Restoration poet and playwright John Dryden in Gerrard Street and Napoleon III in King Street. After early experiments with design, colour and material, the current plaque - a 1912in-diameter blue and white circle made from glazed earthenware - was settled on in 1939.
According to English Heritage, the purpose of blue plaques has always been to draw attention to buildings of interest because of their associations with famous people. As befits such a peculiarly English idea, the criteria for inclusion in the scheme are rather idiosyncratic and far from scientific.
They state that a plaque will be installed when there are "reasonable grounds for believing that the subjects are regarded as eminent by a majority of members of their profession or calling"; or that "they shall have made some important contribution to human welfare or happiness"; or that "they shall have had such exceptional personalities that the well-informed passer-by immediately recognises their names"; or quite simply that "they deserve recognition". There is a final rider: the subject must have been dead for 20 years.
The commemorative plaques panel, which comprises six unpaid historians and people prominent in the arts world, meets three times a year to decide the fate of nominations for new blue plaques which are suggested by the general public. English Heritage staff do some basic research into whether their criteria are met before compiling a potted biography for the panel's consideration. "Most proposals are rejected. We have always rationed the quota of plaques. In the past we put up about 12 per year, but more recently we've doubled that figure to clear a backlog," says Geoffrey Noble, who is secretary to the panel.
If the panel approves a name, English Heritage then chooses the most appropriate property for the plaque - subjects have often lived in several houses, but are granted only one disc - and approaches the owner for consent. "Owners are almost always happy to oblige - sometimes it was they who made the suggestion in the first place. But there have been instances where people have said no. Many years ago there was an objection to a plaque to Winston Churchill because the owner feared it would attract too many visitors. So we kept the file open and when the house was sold we approached the new owner, and the plaque went up," explains Noble.
In special cases, sites of historical interest are also recognised by a blue plaque. Just such an instance occurred in London last month with the unveiling of a plaque at 7 Gower Street to mark the 150th anniversary of the founding of the Pre-Raphaelite Brotherhood there.
The Gower Street house was home to John Everett Millais and his family between 1845 and 1854, and was the place where he and six other artists, including Dante Gabriel Rossetti and William Holman Hunt, met to set out their aims and ideals. The fact that the plaques are considered a significant recognition was testified to by the fact that descendants of Millais, Rossetti and Holman Hunt attended the unveiling ceremony.
The scheme has been repeatedly imitated around London, the country and the rest of the world. English Heritage's decision to promote the official version on a national basis may have something to do with this. The motivation to take the scheme nationwide also reflects English Heritage's national responsibility. "We were aware that, despite many well-run schemes, the position around the country was rather patchy," says Noble.
English Heritage plans to install about 10 plaques in Liverpool over the next year in what is regarded as a pilot operation for similar ventures into other urban centres around the country. Since it launched the idea back in June, there have been a few dozen proposals which will be judged by a new panel early next year. "After Liverpool we will take stock before selecting another city or town. Our intention isn't to pepper the country with blue porcelain. We will remain very selective," says Noble.
So does this selectivity bestow any extra value on a property with a blue plaque? Not according to Ian Peel, who, as a partner of estate agents Knight Frank, has sold a number of properties so endowed .
"A blue plaque certainly adds interest but I'm not sure if you can quantify any added value in financial terms. Most blue plaque properties are interesting houses in their own right, and the plaque certainly gives us another dimension to our marketing," he says.
One problem with the scheme, Peel points out, is that someone familiar to passers-by in 1910 may not have the same recognition-factor now. "The last blue plaque property we sold had two plaques, which is very unusual, but unfortunately both were obscure 19th-century philanthropists. With a more recent celebrity you could perhaps put a premium price on a property and a buyer wouldn't quibble," he says. English Heritage attempts to avoid bestowing the honour on those whose fame is ephemeral by rigorously observing the "dead for 20 years rule". But Noble admits, "The people who are closest to us in time are often the most difficult to judge. Sometimes we leave people a bit longer to let their reputations mature."
Despite the unveiling of a plaque to rock guitarist Jimi Hendrix last year, Noble insists that the blue plaque scheme isn't about to fall prey to the modern mania for celebrity with plaques hoisted to Spice Girls, television soap stars and footballers. "Provided we stick to the 20-year rule, there shouldn't be a problem," he says. And the list of those names about to be honoured with a plaque is suitably reassuring - it includes individuals of such mature reputations as Sybil Thorndike, Nancy Mitford, Will Hay, Dorothy L Sayers, Frederick Delius and Boris Karloff, who, it turns out, was born in Peckham. !