Walk the streets of London and chances are you’ll soon come across an English Heritage Blue Plaque commemorating someone famous.

There are now more than 990 Blue Plaques in London, commemorating everyone from diarist Samuel Pepys to writer Virginia Woolf and comedian Tony Hancock.

The scheme was started in 1866 by the Society of Arts (later the Royal Society of Arts) having been proposed by MP William Ewart three years before. The first two plaques were erected in 1867 – one commemorating poet Lord Byron at his birthplace, 24 Holles Street in Cavendish Square (although this property was later demolished) and the other commemorating Napoleon III in King Street, Westminster (this is now the oldest survivor of the scheme).

Thirty-five years – and 35 plaques – later, the London County Council took over the scheme. It was this body that standardised the plaque’s appearance (early plaques come in various shapes and colours) and while ceramic blue plaques were standard by 1921, the modern simplified Blue Plaque didn’t appear until 1938 when an unnamed student at the Central School of Arts and Crafts, who was paid just four guineas for their troubles, came up with what is now an iconic design.

In 1965, the LCC, having created almost 250 new Blue Plaques, was abolished and its successor, the Greater London Council, took over the scheme, expanding its area of coverage to includes places like Richmond, Redbridge and Croydon. In 1984, the GLC appointed artisan ceramicists Frank and Sue Ashworth of London Plaques to make the Blue Plaques (and they continue to do so).

The GLC placed some 262 Blue Plaques before, in 1986, English Heritage took over management of the scheme. Since then it’s placed more than 360 plaques.

The plaques, which are 495mm (19½ inches) in diameter and 50mm (two inches) thick, are slightly domed in a bid to encourage self-cleaning in the rain.

Anyone can propose a subject for a new plaque – but generally only one plaque is erected per person (although there have been some exceptions to this), only a maximum of two plaques are allowed per building (there are 18 buildings with two), and proposals, if turned down, must wait 10 years before they are reconsidered.

In addition, new Blue Plaques are only erected a minimum of 20 years after the subject’s death, the building on which one is placed must “survive in a form that the commemorated person would have recognised, and be visible from a public highway”, and buildings which may have many different personal associations, such as churches, schools and theatres, are not normally considered.

The Blue Plaques panel meet three times a year to decide on proposals. Among those currently serving on the 12 person body are architectural historian Professor William Whyte, who chairs the panel, award-winning journalist and author Mihir Bose, Emily Gee, regional director for London and the South East at Historic England, and, Susie Thornberry, assistant director at Imperial War Museums.

The plaques don’t confer any legal protection to buildings but English Heritage says they can help preserve them through raising awareness.

Recently unveiled plaques have commemorated pioneering social research organisation Mass-Observation, lawyer Hersch Lauterpacht – who played a key role in prosecuting the Nazis at the Nuremberg trials, and, Dadabhai Naoroji, an Indian Nationalist and the first Indian to win a popular election to Parliament in the UK. Among those being unveiled this year are plaques commemorating anti-racist activist Claudia Jones, suffragette Emily Wilding Davison and Ada Salter, the first female mayor of a London borough.

English Heritage’s Blue Plaques scheme isn’t the only one commemorating people in London. Others include the City of London’s Blue Plaques scheme (there is only one English Heritage Blue Plaque in the City of London – it commemorates Dr Samuel Johnson), Westminster City Council’s Green Plaques and Heritage Foundation plaques which commemorate figures who worked in entertainment.

For more, head to www.english-heritage.org.uk/visit/blue-plaques/.