The 1862 Grade II listed structure carries 3,000 vehicles an hour at peak periods.
The 250m seven span structure with 15 arched ribs of cast and wrought iron, was strengthened to take 40t vehicles.
Close liaison between the contractor J Murphy & Sons, consultant engineer High-Point Rendel and English Heritage ensured the 11.7M strengthening operation remained sympathetic to
the original design.
'We did feel that Westminster was in a special category because of the enormous cost of the strengthening. But it was a tremendous effort,' said Paxton.