Greater London has the highest concentration of listed buildings in the country, with 603 in Barnet alone.

Many of these can now be seen on a web site launched by English Heritage called Images of England (www.imagesofengland.org.uk) which aims to provide a 'point in time' snapshot of every listed building in England.

Listed buildings are buildings that have been protected by the Government because of their special architectural or historical importance. Records of listed buildings are kept by English Heritage, which also deals with recommendations for buildings to be added to the list.

There are now more than 370,000 listed buildings registered, a number that is growing all the time. All sorts of structures can be listed, from milestones and tombs to stately homes and cathedrals, and they are all protected from being demolished or altered without permission.

They don't even have to be old or particularly beautiful as long as they are deemed to be of national importance.

Two good examples of this would be the former control tower at Hendon Aerodrome or the 8ft-deep ice house that tunnels into the ground at St Joseph's Convent School in Hendon, both of which have Grade II-listed status.

Listed buildings come in three grades, with Grade I being of paramount importance to the nation, Grade II* described as buildings that are of outstanding interest and Grade II being of special interest.

Barnet boasts several grade I buildings, including The Free Church in Central Square, Hampstead Garden Suburb, an early 20th Century building designed by the architect Sir Edwin Lutyens.

Many listed buildings (and many that aren't listed) feature English Heritage blue plaques, recording the names and dates of famous people who lived or worked there.

The first blue plaque was erected in 1867, in memory of Lord Byron and, since English Heritage took over the scheme in 1986, it has erected more than 200 plaques.

Even Alexandra Palace has its own blue plaque commemorating the fact that it was the site of the world's first regular television broadcast.

Unlike the listing scheme, the plaques don't signify any particular level of protection for a building, but it is another way in which the heritage of our buildings can be passed on to future generations.

People who own a listed building have to abide by strict rules to prevent the unauthorised demolition or alteration of the structure.

In order to make any changes, owners are required to apply for listed building consent and although the majority of cases are dealt with by the local authority, more important cases are referred to English Heritage or even the Secretary of State for the Environment to ensure the building retains its original character.

In cases where work is needed to preserve the building, English Heritage can sometimes provide grants to help with the cost.

For more information, visit www.english-heritage.org.uk