The first iron bridge ever designed by pre-eminent British engineer Isambard Kingdom Brunel has been found - on the eve of its demolition.

The 166-year-old bridge over the Grand Union Canal was scheduled for destruction to make way for a new road crossing of the rail tracks north of Paddington Station, until details of the bridge's designer were uncovered by chance.

English Heritage's Dr Steven Brindle was researching a new history of Paddington Station. Leafing through Brunel's surviving notebooks he found designs and a record of load-testing for the cast-iron beams of a Paddington canal bridge, dating from 1838.

A spokesperson said that by "extraordinary luck", the bridge was found surviving as the previously inaccessible northern end of the Bishop's Road Bridge, a three-lane bottleneck - about to be demolished.

Now the bridge has been removed from the larger structure it was concealed in, and moved safely away from the construction site.

It is the earliest of only eight surviving Brunel iron bridges in the country.

Top Gear presenter Jeremy Clarkson, a Brunel enthusiast, described the discovery as "sensational".

"Isambard Kingdom Brunel's bridges were the bridges that took us from wattle huts and horses to the world we live in today.

"It is astonishing to think that in a city like London, such an extraordinary part of our industrial past could lie unknown and undiscovered," Clarkson said.

Cllr Colin Barrow, Cabinet Member for Economic Development and Transport at Westminster City Council, said: "We are considering positioning it as a public footbridge over the canal, where it would enhance Brunel's magnificent legacy in this area."