Imagine shopping in London Street with narrow pavements and lots of traffic. Or dodging buses, vans and cars in Gentlemen's Walk. Or traffic still using such narrow city centre streets as Lower Goat Lane.

That is what Norwich could be like if it were not for a broken sewer and the vision and charisma of one planning officer in the 1960s.

At that time there were many pedestrianised streets in Europe but all proposals in the UK to remove vehicles from shopping streets had failed in the face of opposition from shopkeepers who believed that their trade would be damaged by the loss of passing traffic.

All that changed on July 17 1967 when London Street became the first existing shopping street in Britain to be pedestrianised.

This was no brave civic initiative but the result of emergency repairs being required to a sewer that caused London Street to be closed to traffic for six weeks at the beginning of 1965.

Initially, retailers were concerned that their trade would suffer. But it soon became apparent that the opposite was the case: one shop manager observed that his customers liked 'to be able to walk across London Street with nothing more dangerous than a few holes to think about'.

Soon after the street re-opened to traffic, the traders voted 2:1 in favour of pedestrianisation, a proposal strongly supported by the Norwich Society.

But the City Corporation was not convinced. Objections included worries about displaced traffic causing problems in adjacent streets and, strangely, the chairman of the Town Planning Committee doubting whether 'the citizens are going to accept the discipline'.

Fortunately, the City had just appointed a new planning officer, Alfred Wood. Wood understood that the problems were much more serious than the discomfort of pedestrians in one shopping street. With traffic growing rapidly, he pointed out that even a massive road-building programme would not provide a solution but would 'merely create an unending spiral of more cars seeking to use the increased road space... Historic cities, such as Norwich, are particularly vulnerable and it would be unthinkable to sacrifice all the established architectural and historical character order to cater for unlimited motorisation'.

Wood took three members of the planning committee to see pedestrianisation schemes in four cities in Europe. On their return, a three-month experimental closure of London Street was approved and came into force on July 1967. It was an instant success: within a week, restaurants had set up tables and chairs in the street which, according to Wood, 'took on a continental atmosphere as shoppers and tourists pause for refreshment'.

Displaced traffic soon found new routes without problems. A survey showed 90 per cent of people liking the 'Foot Street', Alfred Wood's preferred description. A separate survey by the Automobile Association showed just 4 per cent of its local members objecting while almost half wanted more streets pedestrianised; and the great majority of traders found their takings increased, some by as much as 10 per cent.

A permanent scheme with kerbs removed, the street being repaved, and seats and planters installed was put in place in 1968.

By 1970, 19 other cities in the UK had followed the Norwich example and Alfred Wood had produced a central area traffic plan for Norwich that would extend pedestrianisation throughout much of the shopping area, a plan that continues to influence current thinking with two more streets having been pedestrianised recently, Westlegate last year and All Saints Green earlier this month.

But the battles are still being fought. Alfred Wood's comment about the vulnerability of city centres to unrelenting traffic was paralleled last year when the Director of Community and Environmental Services at Norfolk County Council, Tom McCabe, explained to those who continue to want unrestricted access to the centre of Norwich that 'we have got to acknowledge that it is a mediaeval city'.

The Norwich Society believes that more streets would benefit from pedestrianisation. Perhaps the most obvious is Elm Hill, where the narrow pavements and carriageway make it feel dangerous, discouraging pedestrians from using one of the best preserved mediaeval streets in Britain.

Far more challenging are our long-term ambitions to considerably reduce traffic in Magdalen Street and create a pleasant outdoor area in Castle Meadow in place of its current role as a bus station: neither is going to happen quickly, although we believe that businesses would benefit and the city would become a much more pleasant place.

As its contribution to celebrating the 50th anniversary of the pedestrianisation of London Street, the Norwich Society is organising a free public lecture on July 17 to discuss current trends in the design of public spaces, including the economic and environmental benefits of street improvements.

For details about the event and how to book, see thenorwichsociety.org.uk