It somehow seems perfectly natural, on a warm autumn day in London, to be sipping freshly mixed cocktails in the Permit Room of a former railway goods shed behind King’s Cross, and enjoying a lively discussion on the thorny issue of independence.

After all, we’re surrounded by visual reminders of the difficult separation of two previously joined countries, the ensuing displacement of 14 million people and the deaths of up to two million.

We’re not, however, discussing modern British politics post-Brexit, or the 2014 referendum on independence for Scotland. Instead, we’re marvelling at the upcoming 70th anniversary of the 1947 partition of India in an incredibly authentic recreation of the popular Bombay cafes that back then had been established by a young Zoroastrian immigrant fleeing religious persecution in Persia (now Iran) in the run-up to the declaration of the Union of India. They were known locally as Irani cafes and served affordable chai, snacks and meals to immigrants of all nationalities, religions and class, be they Indian, Pakistani, British, Muslim, Christian, Hindu, Jew or Parsi – who followed the Iranian prophet Zoroaster. They started in 1928 and were at the height of their popularity as India was finding its feet as a newly-fledged nation.

The King's Cross setting is an apt metaphor for travel and human migration, and today attracts a modern melting-pot of nationalities. I spot a group of Japanese hipsters, two elderly Indian women and a team of English businessmen eating, below a hand-written Hindu slogan on the wall: do roti har insaan ka haq (two pieces of bread is every man’s right).

The spirit of integration embraced by the original Bombay cafes – which in their heyday numbered almost 400 and are now down to fewer than 30, with numbers still dropping – is captured in a painted poster on the wall of the upstairs restaurant. It’s a replica of the list of rules of behaviour that were once in every cafe, which speaks volumes about how they encouraged tolerance. No violence, no making mischief; no mendicants. But the last one – “all castes welcome” – has been altered to read “all welcome”.

The faded grandeur of this place is mesmerising. Nostalgic it may be but its relevance to modern times is indisputable.

“All these lovely old Irani cafes were established by immigrants. Unlike the all-British Indian clubs like the Gymkhana, they became refuges for all incomers and helped break down cultural and religious barriers, but they had to regulate people’s behaviour since it was the first time everybody had been able to eat and drink together,” explains Kavi Thakrar, the articulate and thoroughly engaging co-founder (with his cousin Shamil) of Dishoom, the small but popular cluster of inexpensive London restaurants based on these Irani cafes, which next month expands to Scotland with a restaurant in Edinburgh.

“By recreating the spirit of the Bombay cafes we really believe we can do the same again. We believe food can be the glue that binds.”

To prove his point, he says Dishoom holds celebrations for Diwali, Christmas, Eid and Holi – the Hindu spring festival. Some 500 non-Muslims attended the recent Dishoom Eid in London. In the ongoing spirit of inclusion, it donates meals to children in India and London through the Akshaya Patra charity. Such is the obsession with old Bombay that they decline to embrace its modern name of Mumbai.

Thakrar, 34, whose family comes from Gujarat, north of Mumbai, studied at Edinburgh University. He believes “food is definitely political”, but his restaurants aren’t obviously so – apart, perhaps, from their accessible prices aimed at making good food as democratic as possible. The interiors all have different, meticulously researched themes linking their location to their connection to India. “We do it differently every time, and our food is sincere and respectful of its Bombay origins, with a range of signature dishes in each restaurant,” he says. There’s no centralised kitchen; each chef makes everything, including spice mixes, each day from scratch.

The Carnaby restaurant is built around a 1960s theme, complete with reclaimed G-Plan furniture, electric fires and Beatles memorabilia (they even made an LP that plays an Indian version of Jumpin’ Jack Flash and the Savages’ rendition of Born to Be Wild, among others, to emphasise the synergy between British and Indian music of the era). The signature dish here is sali boti, a Parsi classic which is served at Britannia & Co, one of the last remaining Parsi cafes in southern Bombay. Tender lamb is braised in a rich gravy and finished with crunchy sali crisp-chips, then served with buttered "roomali roti" handkerchief bread, made in the on-site bakery.

In Shoreditch the ambience of old Bombay is equally referenced in breathtaking detail. Low-key at street level, you enter a vast, dimly-lit space that is all dark wood, ceiling fans, faded greens and oranges, exquisite marquetry and floral crockery. A separate space, the Verandah, is all lounge chairs, newspapers and breezes which transport you straight back to Colonial India. Diners queue round the block to get in and the restaurant serves 1,000 customers a day.

Small plates – including spicy battered okra fries, a stunning keema pau of minced lamb and peas with a toasted, buttered bun, and bhel, a delicious, moist Bombay mix of puffed rice, nylon sev (thin threads of crunchy pasta) with pomegranate, tomato, onion, lime, tamarind and mint – are priced at around a fiver each.

Mains include a lamb raan, a large, melt-in-the-mouth leg marinated in ginger and garlic, flame-grilled and served whole to be pulled easily off the bone by diners, which will soon become an Edinburgh special when the meat is sourced locally (£22.90). Slow-cooked house black daal (£5.90); a stunning chicken Berry Britannia biryani based on the old Irani cafe recipe and served warm with softly melting depths at £8.90 and nothing like the watery versions we get here; and a murgh malai – flavoursome chicken thigh meat steeped overnight in spices and cream. I'd recommend them all.

There are two Ruby Murrays on the menu: a filling vegetarian mattar paneer at £7.90, and a chicken Ruby with makhana sauce. A pineapple and black pepper crumble, a chocolate pudding with chilli ice-cream and a Memsahib’s Mess (a take on Eton mess, with delicate rose syrup and gulkand) are on the dessert menu, again at extremely reasonable prices.

I didn’t get to try the Dishoom breakfast of bacon naan roll, Bombay omelette, bun maska and chai, which I’m told have become famous since the first restaurant opened at Covent Garden in 2010. Sourcing local bacon – perhaps from Ramsay’s of Carluke – is one of executive chef Naved Nasir’s priorities for Edinburgh. Each restaurant has its own bakery for daily supplies of roomali roti (a soft, handkerchief-thin stretched bread) and naans.

Since chef Nasir is a strict Muslim and doesn’t drink alcohol, we have a watermelon sharbat – a kind of slushed ice drink – and unlimited servings of milky, spicy chai. Neither does he eat pork so another member of the kitchen staff handles the bacon and sausages. Out of deference to various religions, there is no pork or beef on the main menu, though lamb, chicken, fish and eggs – happily, all ingredients raised to high welfare standards in Scotland – feature prominently alongside vegetables.

Signature dishes exclusive to the Edinburgh menu are currently being developed, and are likely to include haggis, perhaps for the keema per eedu (a Parsi dish of minced chicken with chicken liver and fried eggs). “We’re working on two or three Scottish-inspired dishes as there are many similarities in our food,” says Nasir.

Dishoom opens in Edinburgh’s St Andrew Square, in the Category A-listed former 1920s Forsyth’s department store warehouse, later this month under the direction of Thakrar. It will pay homage to Patrick Geddes, the Ballater-born biologist, sociologist, geographer and philanthropist who was also a celebrated town planner and had a big influence on the improvement of both Edinburgh’s Old Town slums and Bombay, where he lived from 1917 to 1924. He also believed in the power of green spaces and locally-grown food to improve diet.

“We didn’t know much about Geddes before this project,” admits Thakrar. “He’s quite obscure but with strong connections to Edinburgh and Bombay. With the help of the National Library of Scotland we’ve found out that he was anti-imperialist and supportive of independence for India.”

Geddes was a pen-pal of Rabindaranath Tagore, the first non-European recipient of the Nobel Prize for Literature whose links with Edinburgh are celebrated at the Scottish Centre for Tagore Studies at Edinburgh Napier University, and there are letters outlining their thoughts on nationalism and Tagore’s protests against British policies in India.

And so we come back to politics.

“Our view is that food should deepen rather than dilute links between countries and cultures,” says Kavi Thakrar. “That’s why Nicola Sturgeon’s views on inclusion as stated in her recent SNP conference speech are very important to us.

“What we’re doing is quite high-brow but it’s also joyous, fun and really accessible.

“In Edinburgh we’ll celebrate Geddes with Scottish botanicals in our cocktails, and the space will feel quite academic, like a college library – a mix of a cafe and a reading room. It will be beautiful.

“After all, the early Indian colonisers were Scottish, so Edinburgh is a natural home for Bombay culture.”

Dishoom Edinburgh’s soft launch (with 50% off food and drink) runs from November 25 until Sunday December 4. 

Dishoom Edinburgh, 3a St Andrew Square, Edinburgh. Visit dishoom.com