The Lynn Area Traffic Study, currently in progress, is looking at the impact of modern-day traffic on the South Gate and what options there may be to divert that part of London Road, as part of the town's urban renaissance plan and the Nar Ouse Regeneration Area scheme.

West Norfolk Council leader Nick Daubney wants to see traffic routed away from the structure and through the small park on the eastern side of London Road near the South Gate.

But he said it depended on the outcome of the surveys and then land acquisitions and negotiations with the property owners affected – so a solution might still be a few years away.

"It would give us a great opportunity to make that whole corner a more pleasant environment and we would have a beautiful civic entrance to the town that wasn't in danger of being hit by a lorry," he said.

"I'm sure that the constant vibration can't be doing it any good. We want to protect the South Gate and make the traffic flow freely."

Volunteers who show tourists round the South Gate reflect that view – and are hoping that something can be done sooner than later.

One of them, Jacqui Sears, said: "This must be the only medieval building in England that has traffic going through it at such a rate and it obviously undermines the building. If it was in York it wouldn't happen."

Lynn's first South Gate was constructed with timber at the request of the Mayor and Burgesses, probably in the reign of Edward III (1327-1377).

A London mason, Richard Hertanger, began work on the present structure of brick and stone in 1437. But he was unable to complete the South Gate for his original estimate, as town records suggest he drank the money away!
Two local builders then took over the task, completing it by 1520. The construction is mainly of brick and limestone, but the upper south face has blocks of Barnack stone from quarries in Northamptonshire.

Tides in 1590 seriously undermined the structure's foundations, but it remained standing and played a major role in the Civil War in 1643 when the town's royalist Cavaliers challenged the advance of Oliver Cromwell's Roundheads. Cromwell's troops laid siege to Lynn and about 80 people died in the fighting.

South Gate used to have a spiked portcullis and the grooves in which it worked can still be seen, along with the holes through which the heavy chains attached to its drawbridge passed.

A gatekeeper, armed with a mace, was elected every year to keep out vagrants and strangers except "those that could give a good account of themselves".

Public hangings were held at the gate until 1783 – including those of an eight-year-old boy called Michael and his sister, aged 11, who were both hanged in 1708 for stealing a loaf of bread.

The small arches either side of the main gate were not part of the original design and were added in the 1840s as pedestrian passageways.

Since London Road was widened in 1899 to help improve the traffic flow, South Gate has straddled just the inward lane. Although designed for people, horses and carts, it is now used every day by lorries, buses and cars.

Major restoration work, costing £80,000, took place on the gate in 1982-83 when new timber floors and roof beams were provided, repairs carried out to the leaded roof and the windows and one of the corner towers strengthened.

Further renovations in 1985 saw a new entrance created from the pedestrian passageway in the west side tower. A new £14,000 circular steel staircase was inserted where the stone one had been removed in past centuries.

Borough council historic buildings officer David Pitcher said there were no floors in the building before 1982 and the only access before 1985 was via a stone staircase in the east side tower, which involved dodging between traffic in the centre of London Road.

The South Gate was open very little to visitors for a long period but in 2003 local resident Alison Dunhill volunteered for the historic post of Custodian of the South Gate and Cleanser of the Muckhills, opening it single-handedly for two summers.

She was then helped by Lynn Civic Society member Ken Hill, and in 2005 more came forward. Last year the list of volunteers peaked at 18 and this year 14 have been taking turns to show visitors around. There is still an opportunity to look inside this Wednesday from 1pm to 4pm and from 10am to 4pm on Sunday, September 9, when it will open as part of the town's Heritage Open Day.