Head south: past the petrol station, the chicken shop and the bodybuilder gym, through a thicket of enormous public housing estates, constructed in varying shades of beige and brown. It's quiet on this stretch of Vallance Road in London's East End, a concrete artery connecting disparate neighbourhoods. A short walk north-west brings you to Bethnal Green Academy, from which three British schoolgirls fled to Syria to join the Islamic State group last year. An equal distance south-west lands you at Fournier Street: home to a different kind of enfant terrible – the British artist Tracey Emin, whose most famous work, My Bed (1999), featured Emin's own authentically unmade bed, strewn with cigarettes and used condoms.

And yet here's your destination: an unremarkable brown brick building, affixed with a circular, cobalt blue plaque: "Mary Hughes, 1860-1941 / Friend of All in Need / lived and worked here 1926-1941".

Was there ever such a lovely descriptor? Mary Hughes was once a stalwart champion of East London's poor. She bought the Vallance Road building in 1926 and quickly converted it into a centre for education, Christian socialism and trade unionism. There, she passed many productive years. But her final days were spent as an invalid, after she was injured by a tram while marching on behalf of the unemployed.

This year, London celebrates 150 years of blue plaques: these tiny, ceramic homages to London's greatest and most eccentric – and on rare occasion, most achingly virtuous – city dwellers. The capital boasts more than 900 official plaques, nodding to notable figures and important historical sites. There are plaques at the home of the World War II code-breaker Alan Turing; the house where John Lennon wrote his songs in 1968; the home of Sir Winston Churchill; the home of Churchill's father, Lord Randolph Churchill; the former hayloft where, in 1820, conspirators plotted to assassinate prime minister Robert Banks Jenkinson, Earl of Liverpool, and his entire cabinet. (They failed.)

History in the streets

The blue plaques offer the historically inclined London wanderer a useful means of navigating the sprawling city and its layered history. To mark the 150th anniversary year, the English Heritage trust, a registered charity that manages the country's historic buildings and monuments, unveiled a blue plaques app (free for download) that locates nearby markers and offers historical context. For locals, the plaques function as collective memory prompts – boldly insisting, in all their blue shininess, that great people did great things here, even if that particular "here" has long since lost its significance.

But what make the system special are those plaques that honour lesser-known London toilers, such as Willy Clarkson ("Theatrical Wigmaker"), Prince Peter Kropotkin ("Theorist of Anarchism") and Hertha Ayrton (a physicist, she invented a fan device used in trench warfare for dispersing poisonous gas).

At 7 Bruce Grove, in the Tottenham neighbourhood of North London, a plaque marks where "Luke Howard, 1772-1864 / Namer of Clouds" lived and died. Howard, the son of a Quaker businessman, earned his pennies as a pharmacist, but his passion was the skies and he soon became an accomplished amateur meteorologist. In 1802, he wrote a modest 32-page pamphlet that proposed a classification system for clouds: cumulus, stratus and cirrus. The paper was eventually published in an academic journal, and he was catapulted to scientific fame. His many admirers included Goethe, who went so far as to send Howard gushing fan mail.

English Heritage continues to accept nominations for plaques. This year, the playwright Samuel Beckett got his due, as did Fred Bulsara, aka the Queen frontman Freddie Mercury, whose family moved to west London in 1967 after leaving Zanzibar, Tanzania. A blue plaque now marks the home where a young Mercury reportedly spent hours in the bathroom styling his hair.

Since 1984, the plaques themselves have been made by the ceramists Frank and Sue Ashworth, who kiln-fire and glaze each nameplate – 50 centimetres in diameter, five centimetres in thickness, using a base blend of ball clays, feldspar, sand and grog – in a studio in Cornwall, where they replicate the original lettering used by long-ago plaque designers.

In this physical process, tradition trumps novelty.

But in other ways, the plaque program is bending to the times. This year, it was revealed that only 4 per cent of London's blue plaques commemorate black or Asian individuals, and just 13 per cent are dedicated to women.

In an era of contested memory and memorials, critics have accused blue plaque commissioners of doling out posthumous pats on the back to Great British Men. In response, English Heritage has acknowledged its "historic blindness" and called on the public to nominate more diverse candidates, so that future London walkers can ramble through a more inclusive, cobalt-blue-laid nostalgia.