A monumental achievement

The history of London is gradually moving full circle to where it was in this photograph of St Paul's cathedral (left) taken by an anonymous snapper from Campbell's Press Studio in 1905. Here are those decorative Victorian gas lamps that, plucked from the capital's streets in the Fifties and Sixties, made their reappearance in middle-class London "villages" in the Eighties and Nineties after Victorian values had been reimposed by Mrs Thatcher's nanny state.

Here, too, is the deregulated, open-top bus, a two-horsepower predecessor of today's 200hp, open-top, deregulated tourist buses that throb and bray past Wren's masterpiece. Advertisements on the clapboard sides of the horsedrawn bus state the case for Nestle's Milk and Borwick's Baking Powder, not perhaps as popular today as they were 90 years ago, but still available at corner shops. Blue-coated policemen, City gents and Cockney traders inhabit this 1905 streetscape as certainly as they do today.

This familiar image is just one of more than 75,000 photographs of London's past now available for public inspection and use at the new West End office of the National Monuments Record.

The NMR, compiled by the Royal Commission on the Historical Monuments of England (founded three years after the Campbell's Press Studio shot of St Paul's was taken) is a treasure trove of architectural and urban memorabilia, most of it on glass plate andcelluloid. Known and coveted for many years by architectural historians, writers and buffs, it has long been hidden away in a maze of secret rooms where the indecent haste of everyday life was all but forgotten. Should a reprint of a photograph be required for publication in a magazine, an anguished editor might have to wait weeks for the precious image to arrive.

Now, a breath of fresh air has blown through the archives of the NMR. On Monday, it is even holding a public open day, when visitors can "interrogate the national collection", covering buildings, street scenes, archaeological sites, aerial photography and maritime sites. High-speed fax links between the NMR's new premises in Marylebone and its record centre in Swindon promise to bring historic images to your attention in a matter of minutes rather than the weeks of yore.

Visitors will also be able to meet the compilers of the magnificent Survey of London, an extraordinary enterprise that has led to the history of the capital's streets being uncovered almost building by building. The findings are published in a series of magnificent books that, beginning before the First World War, has yet to be completed.

The NMR can tell you if your house, or any other building you care about, is listed and whether your local park is included in the Register of Historic Parks and Gardens for England.

It can also offer help and advice if a historic building near you is under threat of demolition. In fact, the chaps and chapesses at the NMR need your help too; should you know of a building under threat, the NMR will ensure that it is recorded, photographed and that the people and authorities able to save it from oblivion are informed. Who knows...by opening up a mine of information and images, the NMR might also be prising open a Pandora's box. St Paul's Cathedral, by the way, is likely to stay with us, with gas lamps and horse buses on the way by the turn of the century: photograph it now before it is no longer possible to distinguish a St Paul's streetscene in 1905 from one recorded for posterity in 2005.

National Monuments Record, London Search Room, 55 Blandford St, W1 (071-208 8200). Open Mon-Wed 10am-5.30pm, Thur 10am-7pm, Fri 10am-5pm. Public open day Monday 23 Jan 10am-4pm