A retired civil engineer who helped design Spaghetti Junction has blasted “ludicrous” plans to increase motorway speeds to 80 mph.

Roy Foot, now aged 83, played a key role in the development of the world-famous landmark which began life as the Gravelly Hill Interchange and became Europe’s largest motorway junction.

But Mr Foot, who worked for nearly four decades at London-based civil engineers Williams and Partners helping develop the M1, M6 and M5 as well as Spaghetti, says the 70 mph speed limit was “fundamental” to the design of the junction.

Mr Foot, who lives in Kent and is a civil engineer of 36 years’ experience, said the radius of curves, their superelevation, the gradients and the sight lines of motorways were all determined with a top speed of 70mph in mind.

He said the figure ”was not just plucked out of the air”, and was “fundamental to our designs”.

Mr Foot told the Post: “You cannot drive at 70 mph around Spaghetti Junction, let alone 80 mph – 80 mph is fine along lengthy stretches of motorway where you have got long stretches of road.

“But in other places, you can’t do it and Spaghetti Junction is one of them. In general I do not think it (an increase to 80 mph) would make a hell of a lot of difference.

“Our brief was to take the motorway as close to the heart of Birmingham as we could and that is what we did. It occupies 30 acres and is a very compact junction.

“It was a three-year contract and it went six to nine months overtime because of having to do all the checks.

“My point is that motorways were designed for 70 mph in the same way that Spaghetti Junction was designed for a traffic capacity of 75,000 a day.”

Traffic figures estimate the Birmingham landmark currently takes double that capacity.

Spaghetti Junction was opened on May 24, 1972, by the then Environment Secretary Peter Walker, who described it as the “most exciting project in the history of the road system.”

Known officially as the Gravelly Hill Interchange, it was first dubbed Spaghetti Junction by Roy Smith, the municipal correspondent of the Post’s sister newspaper the Evening Mail for many years.

Mr Foot explained: “One of my colleagues objected to the name because spaghetti is a formless mass which just drops on a plate. But it’s a great name – it stuck.”

It cost £10.8 million to build and required the demolition of 160 houses, a block of luxury flats, a factory, bank, pub and public toilet to make way for it.

A total of 11 years was spent in the planning and design of Spaghetti Junction and it took another four years to complete.

As the joining point of several roads, two rivers, two railway lines, three canals and electricity lines, the site was of such strategic importance it was supposedly on a list of Russian nuclear strike targets during the Cold War.

Mr Foot retired as managing partner from Williams and Partners, who had an office in Hagley Road, Birmingham, in 1992.