Speaking to BigHospitality, Marc Francis-Baum, who founded The Diner in Shoreditch in 2005 with Andreas Akerlund and Patric Franzen, revealed the team were set to complete on a deal today (Thursday 11 July) to buy the Fire & Stone site on Horner Square.
When the venue is re-opened under the brand, it will become the seventh diner in the group which now has restaurants in Soho, Camden, Covent Garden, Islington and on Gloucester Road which became the most-recent opening when it launched in May.
An eighth restaurant in Kensal Rise was sold this year.
"We should get 120 covers in there (Old Spitalfields Market) and more outside so it is quite a big site - a similar size to the Soho diner," Francis-Baum said.
The same team who run The Diner brand under the Goodlife Group company also own restaurant and bar operator Barworks as well as Camden Town Brewery.
Building work is currently underway on a site in Farringdon for the next opening under the Barworks brand following the recent sale of The Hoxton Bar and Kitchen for £1.9m.
At the time of the sale, Francis-Baum said the proceeds would be used to fund the expansion of Barworks and The Diner - he said the latter could potentially expand at the rate of three a year.
Speaking today, the businessman confirmed he was always on the lookout for venues that could become diners.
"We are looking actively in Dalston. The only problem we have got is we are actively looking on the bar side and for brewery pubs too - we are fighting and expanding on three fronts.
"It is good in a way but if we put all our eggs in one basket and just concentrated on the diners we would probably be a lot faster.
"We see sites and go 'yes that is definitely a diner' or 'that is a great pub/bar site'," he explained.
Key members of the operations team for The Diner pay regular research trips to the USA in order to refresh both the food and cocktail menus - sliders were first available some two years ago before the recent trend for the mini burgers kicked off.
Recent menu additions include lamb slammers, buttermilk fried chicken and gravy and a number of new cocktails and craft beers.
Despite the recent boom in American-themed restaurants, Francis-Baum said he believed The Diner's extensive menu and varied breakfast offering differentiated it from other burger restaurants masquerading as traditional diners.
"We sell a lot of burgers of course but our 'thing' has always been that we are not a burger chain, we are a diner. You can get breakfast, lunch and a variety of main meals.
"We have always loved English greasy spoons. Doing that concept would be quite difficult although I am sure I will be able to create it one day but the American diner, with pancakes and a whole array of breakfast dishes which you can eat all day, works," he added.