Archaeologists have found Britain's oldest properly engineered road, and the discovery could change the way we look at a key aspect of British history. Now, many of the country's key A roads – long thought to be Roman in origin – could now turn out to be substantially more British than scholars had thought.

The discoveries, in Shropshire, suggest that ancient Britons were building finely engineered, well-cambered and skilfully metalled roads before the Emperor Claudius's conquering legions ever set foot in Britain in the middle of the 1st century BC.

So far, they have found two sections, totalling 400m, but their alignment suggests that the road connected two key political centres of the Iron Age tribal kingdom of the Cornovii, the Cornovian "capital", the Wrekin hill-fort near modern Telford, and Old Oswestry hill-fort, near modern Oswestry.

The discovery of the road, revealed in the BBC History Magazine, is for the first time demonstrating the sophistication of British Iron Age cross-country road construction.

First a brushwood foundation (made of elder) was laid down. Then a layer of silt was placed on top of the brushwood, and finally a layer of cobbles was set into the silt to provide a good surface. A kerb system, kept in place by timber uprights, was even constructed to prevent the Iron Age highway slumping. The road was regularly maintained, and resurfaced at least twice during its life.

The excavations, funded by the UK's largest building materials company, Tarmac, have also provided remarkable information about the wheeled traffic using the Iron Age highway....