(dedicated of course to Wilko Johnson 1947-2022 who bought a whole lot of Southend joy to London and music in general. )
One of the annoying things about bricks used in London, or anywhere, is that the stamps which identify them, are not visible as they are almost always in the ‘frog’.  And yes all or almost all, these stamps have been catalogued and identified so if you can see the stamp you will almost certainly know where a brick was made and what from. 
So unless there is a broken wall or the house is being demolished you won’t get to see them. Some bricks are known via the developer or contractor and from historic records. But garden walls of waste brick walls where bricks are not laid conventionally do however offer a chance of a glimpse of a stamp and hence the manufacturer though sadly the bricks themselves are not always stamped.
And a garden wall to the south of Wanstead Park at the junction of Northumberland Avenue and Ingatestone Road does show us stamps and so tells us who made the bricks and where they have come from as they are clearly stamped with a ‘MH’.
Milton Hall bricks
And we know that MH was the stamp of Milton Hall, a brickmaking company set up initially in central Southend in the late 19thC and moving in 1932 to a new site in Great Wakering a village to the north east of Southend, both on the Essex brickearth, and in an area where many bricks were sent to London from the late 19ths to the second half of the 20thC initially by barge but then by train.
The company was set up in 1878 by a local self-made man, Thomas Dowsett “ … the first mayor of Southend in 1892 .. Thomas Dowsett’s business was centred at first around a furnishing and general ironmonger’s shop in High Street, Southend. He later diversified into housing development and was one of the founders of Milton Hall (Southend) Brick Company Limited (1878) and Southend-on-Sea Estates Company Limited (1906).”   The Milton Hall company seems to be named for the historic Manor of Southend. 
It’s not clear where they started but they have a brickworks by 1895 just to the east of Southend Victoria Station, a spur of the Great Eastern, which opened in 1889, with sidings into the station for no doubt sending bricks into London which by 1920 is quite extensive. After closing in 1932 the Southend Stadium, where Southend United played between 1934 and 1955, was built on the site.
The site is now a retail park with no apparent links to the brickworks, though intriguingly one of the roads that replaced the brickworks in the 1930s was, and remains, Redstock Road which sounds as if it is named for the brickworks.
“The new stadium was built on the site of the Milton Hall Brickworks in the All Saints Ward and featured two main stands, the east stand which would later have a restaurant and the west stand with covered seating, the remainder of the stadium being uncovered terracing. The Milton Hall Brick Company Ltd had just opened the Star Lane Brickworks in the nearby village of Great Wakering allowing the sale of the older Brickworks located between the Redstock Road to the north, Maldon Road to the south and Sutton Road on its east side….The last meeting was held on Boxing Day 1985. Two months later the stands and terracing were demolished making way for a retail park.” 
The later Star Lane brickworks at Great Wakering which opened in 1932 lasted for 70 years only finally closing in the 2000s. The streets that have replaced it are rightly named for the works, with a Brick Road and a Kiln Road.  
Strangely the Milton Hall company still appears to have some legal existence even though it is owned by brick making giant Hanson, who still make bricks in that name. 
But what are these bricks doing in Wanstead? And when would they have made the journey from Southend to Wanstead? The house on Northumberland Road appear to have been built in between 1893 and 1913 – the streets are not on the 1893 OS map, but on the 1913 map – and their style looks Edwardian so probably nearer the later date.
But Wanstead also had brickworks  exploiting no doubt a local brickearth.  So why import from Essex when you could build from local brick? There were brickfields south of Aldersbrook Road in Wanstead Flats in 1875 though which closed in 1881 and supplied bricks for Bethnal Green , but also to the north, a stones throw from Ingatestone Road, in 1895. By the 1913 map the streets and houses are built and the brickworks has gone. It’s seems likely that at least the structural, if not facing, bricks would have been made at these brickworks. And yet the garden wall is of bricks from Southend.
The answer to this conundrum seems to be that, looking at the houses it can be seen they mainly built of ‘yellow’ London Stock Bricks but they also use what look like Soft Reds for facing the fronts of the houses, which apparently Milton Hall was famous for. Is it probable that the bulk of these houses was built from local London Stock brick, though by this time lots of London Stock Bricks were already being imported from the Kent and Essex brickearth lands, but that the facing bricks were trained in from Essex and with them some waste bricks for the garden walls.
This quote is more recent but may reflect older manufacture, as would the naming of the road in Southend, Redstock. “Brick was made at Rochford [ near Southend ] from at least the 1430’s and the abundance of ‘brick-earth’ throughout the area supported a significant local industry. There were many brick manufacturers locally in the 19th century, with the last of these, the Milton Hall company, closing its works at Cherry Orchard Lane in the 1990’s. The loss of their products has been a blow to building conservation, as their soft reds were the best general purpose brick for use in Essex.” 
And indeed Forterra, who took over London Brick, still supplies a red brick called Milton Hall “The Milton Hall Medium Red brick, manufactured by Forterra, is a thrown / stock / soft mud brick that is red in colour with a light texture. As a facing brick, the Milton Hall Medium Red brick is commonly chosen for its aesthetic qualities, and will provide a red, light textured façade.” 
Wanstead Flats Anti-enclosure protests
Wanstead Flats is famous for it’s 1871 mass protests against enclosure, the result of which would have been large areas of the common land part of the historic Epping Forest, being built in, where 1000s of East Enders and east Londoners pulled down the enclosure fences
“THE DESTRUCTION OF FENCES happened later in the evening. Close to nine o’clock an incident occurred which changed the whole aspect of affairs, and the fence around the inclosure at the side of the Flats near the Foresters’ Arms, and quite close to whore the meeting had been held, was destroyed in the twinkling of an eye. A man, while seated on a rail of the fence, was asked by a comrade to go home; he demurred, and his friend pulled at him to make him get down; the rail shook and in a moment half a dozen hands brought it to the ground. A dozen hands laid hold of the next; it gave way; in a minute there were fifty persons pulling energetically, then a hundred, then hundreds. The sound of the breaking up of the railing – for they were smashed into fragments as they were got from the posts – sounded like a continuation of the file-firing of the volunteers, and hundreds of people rushed up from all parts of the Flats and from the side roads and public-houses. In five minutes the fence around the inclosure was almost wholly destroyed.”
Read more at https://pasttenseblog.wordpress.com/2019/07/08/today-in-london-riotous-history-1871-1000s-demolish-enclosure-fences-on-wanstead-flats/
The Flats was saved again from being built on in the 1940s https://pasttenseblog.wordpress.com/2021/12/11/housing-vs-open-space-the-wanstead-flats-campaign-of-1946/
This wall is just to the south of Wanstead Park,  itself a great place to visit and to see the ruined Grotto currently under restoration in on the corner of Northumberland Road and Ingatestone Road in Aldersbrook. 
Southend of course is great to visit at any time! https://www.visitsouthend.co.uk/
 https://pomanda.com/company/00012289/milton-hall(southend)brick-company-limited(the)  https://www.newhamheritagemonth.org/records/brickfield-newham/
 https://data.bgs.ac.uk/id/Lexicon/NamedRockUnit/BRK  https://www.guardian-series.co.uk/news/17003484.wanstead-flats-fire-uncovered-remnants-fascinating-history/