The milestone keeps the bridge project on course to open in the autumn, according to project engineers.

Nicknamed Webster, it has been working on the south approach viaduct for around 10 months, slowly creating the reinforced concrete deck.

The final pour was a 28-hour operation – 1,133 cu m of concrete was being poured into the giant mould to complete the deck of the south approach viaduct.

Webster is one of two movable scaffolding systems, specially designed and built to construct the curved viaducts leading to the Mersey Gateway Bridge.

The northern approach road machine completed its run five months ago.

It has now been moved back one span and will slowly be dismantled over the next couple of months before being transported to Bratislava to join its fellow MSS Trinity, which is helping to build a new bridge over the River Danube.

Webster is 157m long and 8m high. It is 22m across at its widest point and weighs 1,700 tonnes.

In total, since it started work MSS Webster has constructed eight spans of the south approach viaduct using 9,205 cu m of concrete, equivalent to filling four Olympic-sized swimming pools.

Hugh O’Connor, General Manager for Merseylink, said: “To have reached this landmark just 10 months after building Webster is great news for the project.

“The viaducts on either side of the river are huge structures in themselves, with the south approach viaduct requiring a considerable degree of engineering and construction skill to build, as well as using a huge amount of material.

“This final pour on the south approach viaduct means we’re getting closer and closer to completing this iconic bridge.”