Shockingly small flats that apparently measure as little as 3.6 metres by 3.6 metres (12ft x 12ft), residents packed in “like sardines”, a busy six-lane highway just yards away, broken glass and rubbish strewn all around outside ... is Newbury House in east London the 21st century version of a Dickensian slum? Or is this simply the harsh reality when you live on a small island that’s desperately short of housing?

Across the country, office buildings are being converted into “apartments” that are in some cases smaller than the size of a typical bedroom, and fall far short of national space standards. These office-to-residential conversions are controversial because they don’t require planning permission – and there’s growing concern in some quarters about poor-quality accommodation, overcrowding and a lack of usable outdoor space.

Now a leading architect who is one of the London mayor’s “design advocates” has named and shamed what she claims is “one of the worst examples” she has ever encountered: a tatty-looking seven-storey former office block next to the A12 in Ilford, east London, which has been converted into rental flats.

Land Registry records show that Newbury House is owned by a company based 4,000 miles away in the British Virgin Islands, which could well be pocketing several hundred thousand pounds in rent a year – not bad for a property it bought for £1.4m five years ago.

In a comment article for a building design website, Julia Park said Newbury House represents “a new low” in office-to-residential conversions and that “no one should have to live like this”. However, she adds that this is by no means an isolated case. She has written to the communities secretary, the housing minister and the London mayor, Sadiq Khan, expressing her concern.

Many of those walking past this sliver of a building probably don’t even know there is anyone living there, as no one has taken down the signs for long-gone companies and the “staff” car park. However, documents show that proposals to turn the building into flats were waved through by the local council in 2014.

Architects’ plans for he smallest of the proposed studio flats in Newbury House. Photograph: Redbridge Council

The conversion appears to have gone ahead as planned, which means each of the six upper floors is now made up of 10 self-contained studio flats. So that’s 60 flats. The architect’s drawings describe 18 of the studios as “singles” and 42 as “doubles”.

According to the plans, the smallest singles are just 13 sq metres – that’s a room just a fraction bigger than 3.6 metres by 3.6 metres – while the smallest doubles are 14.7 sq metres. Yet the government’s own space standard – known as the “nationally described space standard” – states that the minimum floor area for a new one-bedroom one-person home (including conversions) is 37 sq metres, and for a one-bed two person home it is 50 sq metres. While these minimum sizes are not compulsory, they do apply in London, but only to schemes that go through the planning system.

‘No one should have to live like this … it is inconceivable that living in these conditions could be a positive choice’ Julia Park, architect

Park, who is head of housing research at architects Levitt Bernstein, stumbled on Newbury House while in the area for a site visit on a blazingly hot day earlier this month. There were curtains drawn across many of the open windows, and she could hear voices from inside, including those of children.

It is understood Redbridge council has been using Newbury House for temporary accommodation since December 2017. The council uses it to house single people while they wait to get a social housing place, and also young people leaving care.

In her letter to the housing minister Kit Malthouse, Park says that, assuming the plans were implemented, “all of these studios are offered as self-contained accommodation. Residents are expected to live (sit, cook, eat, sleep and bathe) in one room with a small shower, WC and basin in the corner. No other space is available to them apart from the corridors, stairwells and lifts ... Half [of the flats] face north and receive no sunlight, and half face south and receive full sun.”

She adds: “I do not know who lives here but I am concerned that some may be vulnerable people on low incomes. I say this because it is inconceivable that living in these conditions could be a positive choice for anyone.”

One resident said Newbury House residents were ‘packed in like sardines’. Photograph: Martin Godwin/The Guardian

Guardian Money paid a visit to Newbury House this week. It is right next to the A12, with all the pollution and traffic noise that that entails. We were told we couldn’t come into the building to knock on residents’ doors, and shortly after that we were notified that we would have to leave or the police would be called.

The building looked very shabby, and the small area of outdoor space was strewn with rubbish including large amounts of broken glass. Looking up at the flats, we could see windows propped open with fizzy drink bottles and wooden cooking spoons, and hear music playing. We managed to give our phone number to one of the residents before being told to leave, and he later called to tell us about life in Newbury House.

The man, who did not wish to give his name, told us he had been housed there by the council. He said the residents were “packed in like sardines”, and added that many of the people living there had “issues”. He said there were 10 flats on his floor, and six floors of accommodation.

Asked about his flat, he said: “It’s very small – very substandard to what the government requires.” He added that there was no ventilation.

The man also said the building had become a “crime magnet,” with fighting and drugs, and added: “I’m just worried someone is going to be killed.”

His account was backed up by a notice pinned to the wall of the foyer that was spotted by Money which said there had been complaints of antisocial behaviour including drug-dealing and “weed smoking”.

Documents relating to the building conversion state that the developer was Dorchester Estates, which describes itself as a “boutique real estate company” with branches in London and the Middle East. However, Dorchester Estates told us it was the managing agent. A Land Registry search found that the building’s registered owner is a British Virgin Islands company called Newbury House Ltd, which gives its address as Trident Chambers, contactable via a post office box number in the islands’ capital, Road Town.

During the past few years there has been a frenzy of office-to-residential conversion activity in some areas. This boom is largely down to the fact that in 2013 the government relaxed the rules to allow office buildings to be turned into housing without the need to go through the planning process. These so-called “permitted development” conversions are also not required to meet space standards.

Newbury House is next to the busy six-lane A12. Photograph: Martin Godwin/The Guardian

However, in a report published in May this year, the Royal Institution of Chartered Surveyors (Rics) said its research into the conversions had uncovered some examples of “very poor housing”. It added: “Interviews with residents revealed their concern regarding developments with large numbers of children living in them, that were overcrowded and had no play space on site or nearby. These developments were also exempt from making contributions to local authorities so that they can provide this.”

One resident of a former office in Croydon told the researchers: “I’m speechless. How can this be allowed in a civilised country? It’s so wrong. The politicians who allowed this need to come and live here. It’s a total nightmare.”

The Rics report added that all the indications were that the conversions were “highly profitable” for developers. So how much money is Newbury House’s owner making from those living there? That’s hard to say. But it could potentially be several hundred thousand pounds. Let’s say there were 60 people living there, each entitled to the local housing allowance (the name given to housing benefit for private tenants) for a one-bedroom home in that postcode, which adds up to £8,332 a year, or £4,024 for those under 35 living on their own. LHA helps cover the cost of rent and is usually paid to the individual, but a council will sometimes make the payment direct to the landlord.

Even 60 lots of the lower figure, with nothing added on top, would add up to £241,000 a year.

Redbridge council told us it had a “comparatively small” social housing stock, and that people could wait a long time for a home to become available. “Like much of London, we also have high levels of arising homelessness, and we need to find good-quality and affordable solutions as temporary accommodation and private sector options to meet that need. Newbury House is part of that provision for single homeless households.” It said the government “needs to do more to help us realise our ambitions”.

Britain’s smallest houses

The average total floor space of privately owned Sheffield houses was 61.2 sq metres. Photograph: David Sillitoe/The Guardian

Sheffield is home to the UK’s smallest houses, while Cambridge’s are the biggest.

That is the headline finding of a new survey which will add to the debate on so-called “shoebox” homes. However, there may be caveats attached.

The research by LABC Warranty, which provides warranties for new-build homes, used data from property websites Rightmove and Zoopla to analyse house sizes within a five-mile radius of 20 UK cities.

It said that in Sheffield, the average floor space of a privately owned home was 61.2 sq metres.

The researchers collected data including the size of the living room, kitchen, master bedroom and bathroom, as well as determining the average number of bedrooms and whether the property had access to a garden. However, it appears the analysis did not include certain areas, such as a hallway or staircase, which means it may underestimate the true picture.

The three cities with the next-smallest average house sizes were Southampton (64.9 sq metres), Bristol (65 sq metres) and Glasgow (65.2 sq metres). Meanwhile, the figures for London, Manchester and Birmingham were 65.7 sq metres, 67.2 sq metres and 69.9 sq metres respectively.

The two cities with the largest typical house sizes were Cambridge (71.8 sq metres) and its academic rival Oxford (70.7 sq metres).

Other findings included:

• Almost 74% of the homes surveyed had either a private or shared garden.

• The average UK home has 2.6 bedrooms.

Earlier research claimed that Britain’s new-build homes were already the smallest in Europe.

And in 2015, research from the Royal Institute of British Architects (Riba) showed that more than half of the new homes under construction were too small to meet the needs of those who buy them. It found that homes in Yorkshire were the smallest in England.