The drive to improve London’s transport links before the 2012 Olympics has brought an unexpected bonus for the museum dedicated to the country’s greatest engineers. For when the oldest part of the Tube system, the Thames Tunnel on the East London line, closes for renovation next month (Dec 23), the contractors will include an extra platform in their work - one that will more than double the space available to the Brunel Museum.

The museum is based in the Engine House in Rotherhithe built for the giant steam pumps that raised water from the diggings. But its main exhibit is the tunnel itself. Hailed as the eighth wonder of the world when it opened in 1843 after 18 years of excavations, it was the first tunnel to run beneath a navigable river and the first to be dug using the shield technique that remains to this day the accepted method of tunnelling through soft ground. It was also the only project on which Sir Marc Brunel worked together with his more celebrated son Isambard Kingdom Brunel.

While the main task of the contractors, Balfour Beatty and Carillion, is to renew track and extend the line to form a north-south link to the Olympic site, they will also construct a shelf at the bottom of the 50ft-deep brick shaft, the original entrance to the tunnel workings beside the engine house. From this platform, through a glass panel only feet above the line on which new trains will start running in 2010, visitors will get a close-up view of both the pioneering construction and its modern use.

A feasibility study for the shelf has already been completed by Transport for London, which enthusiastically supports the idea and is now working on the detail design.

“The Brunels were two brilliant men who pushed back the frontiers of the possible. Their engineering was the cutting-edge technology of its time,” says Robert Hulse, curator of the museum. “They were the embodiment of resourceful and innovative engineering that set out to find answers to problems that weren’t even dreamt of before. This development will enable many more visitors to get a close-up view of their work.”

Mr Hulse announced the agreement last week to a meeting of the Tunnel Club, a group of engineers, architects and historians who gather at the museum each year to mark the anniversary of the “Underwater Banquet” - a feast held beneath the river in the part-completed tunnel 180 years ago to impress its scale and safety upon the City bankers of the time and rescue the Brunels’ first great tunnel project from bankruptcy. Members of the Tunnel Club, who include Professor Dan Cruickshank, the broadcaster, Piers Gough, the architect, and Sir William McAlpine, the engineer, are now enthusiastically hoping that the temporary closure of the line might give them a chance to restage an underwater banquet, something not possible with Tube trains running through the tunnel.

The Engine House displays, on loan from the Ironbridge Gorge Museum, a painting of the 1827 Underwater Banquet by George Jones. The elaborate feast, with the imposing arches draped in crimson, tables set with silver and crystal and rousing music from the Coldstream Guards band, was an extraordinary public relations exercise staged by the 21-year-old Isambard Brunel to revive confidence in the project after an interruption due to flooding.

When the tunnel was eventually completed and opened to pedestrians, two million people visited it in the first year. The arcade beneath the Thames was lined with shops and food stalls and became a fashionable curiosity. But a shortage of funds prevented completion of the ramps that were to provide entry to horse-drawn transport. As the novelty wore off and visits grew less fashionable the brick arcades became the haunt of prostitutes and East-End cutpurses.

It was handed over to the railway as the Tube developed and the first trains ran through from Rotherhithe to Wapping on the North bank of the Thames in 1869. The line now carries 14 million passengers a year. While the shaft on the North bank was utilised for the spiral staircase giving access to Wapping station, the platforms at Rotherhithe were built farther back from the riverbank and the shaft there has stood empty for more than 100 years.

Since the 1200-ft long tunnel was restored in 1998, the museum has taken more than 6000 visitors on guided tours by Tube train when the brick arcades alongside the track are floodlit. Although there is a programme of tours ahead of the tunnel’s Christmas-week closure, such opportunities are limited when the line is running at capacity. The new platform will give visitors a chance to see the tunnel even if they have no time for a Tube ride.

“Only a few years ago the museum was open just one day each week and visitors were counted in hundreds. With the extra space available due to this development we hope visitor numbers will reach six figures a year,” says Mr Hulse.

Brunel Museum website