A television documentary will explore how feats of intelligence and espionage during Tudor and Stuart times shaped Britain's culture, religion and architecture.
Tracy Borman, chief curator for Historic Royal Palaces, said some of the landscapes that have come to characterise the country would have looked much different were it not for the James Bonds of yesteryear changing the course of history.
The author and historian said an opulent palace fit for James I's daughter Elizabeth might have taken the place of the Palace of Westminster if Guy Fawkes's gunpowder plot had succeeded.
Catholic monasteries would have become widespread in London if Henry VIII - backed by right-hand man Thomas Cromwell and his network of aides - had not revolutionised religion in this country.
And if England had become a satellite of Spain or France after being defeated by the Spanish Armada or Napoleon, there would have been significantly less investment in London all round as it would no longer be a capital, Dr Borman said.
The research and accompanying artist's impressions of the landscape were conducted to celebrate the launch of new series History's Ultimate Spies which airs on TV channel Yesterday on Friday.
Dr Borman said: "In the Tudor and Stuart periods, England was under tremendous pressure from the Catholicism of mainland Europe, and was a country in transition.
"These religious tensions birthed scores of assassination attempts from within and declarations of war from elsewhere, and the role of Britain's spies should not be underplayed when discussing how history eventually unravelled."
Adrian Wills, Yesterday manager, said: "Londoners are rightly proud of our city's most famous landmarks, but it is staggering just how different the capital's skyline might have looked had it not been for the work of the James Bonds and Ms of yesteryear."
:: History's Ultimate Spies will be shown on the Yesterday channel at 10pm on Friday October 16.