Round tower churches are one of the most distinctive features in the Norfolk countryside - with many thought to date from Anglo-Saxon times.

Norfolk has the lion's share of the national total of about 175 round tower churches with a further 42 in Suffolk plus a handful in Essex and Cambridgeshire.

It was 40 years ago that one enthusiast, the late Bill Goode, founded the Round Tower Churches Society, and next Saturday, members will hold the annual meeting at St Peter's church hall, Gunton, Lowestoft, where it all began.

Over the past four decades, the society has grown and now has more than 500 members from around the world. It has provided almost £150,000 to safeguard and maintain these striking churches over the years. 'It would be entirely fitting if, as seems probable, we reach a total of £150,000 in our 40th anniversary year,' said the chairman Stuart Bowell.

At last year's annual meeting, the long-serving treasurer, Dick Barham, of Old Catton, reported that 14 churches had been given grants of £16,500. It also included the largest single grant in the society's history of £5,000 to help with the re-thatching of St Mary the Virgin, Cranwich, near Mundford.

This same church also received the society's first grant, £20, half a century ago to help pay for removal of the slate roof.

Although efforts had made several years earlier to found a society, it was not until September 1 1973, that it became a legal entity. More than a year earlier, a round tower church, St Andrew's, Letheringsett, near Holt, had been brought to national attention when it was featured by the Royal Mail to mark British Architecture 1972. The 5p stamp helped to raise the profile of these round tower churches.

Mr Goode had taken up photography as a hobby in 1965 when he acquired a new camera, and he soon started visiting and recording round tower churches. 'I read some books about round-towered churches and I found the writers were often contradicting themselves.

'That challenged me to find out what was right,' he told the EDP in 1994.

As the EDP subsequently reported: 'He readily admits he didn't even know how many of them there were... and became hooked on the mystery, the beauty and the character of these remarkable buildings.'

For Mr Goode, who retired as a television engineer for Pye in Lowestoft in 1975, these mysterious and beautiful churches were to become a consuming passion. Self-taught, he studied their architecture and decided to start recording and measuring them, using a couple of washing lines which were lowered from the top of the tower to measure the height of each.

With his wife Ada he travelled thousands of miles in an orange Volkswagen Beetle – complete with 19ft ladder on the roof.

Mr Goode also found that many churches were in very poor condition and that money for repairs was short. Then, using £2,000 of his savings, he published a book, East Anglian Round Towers and their Churches in 1980. It was a financial success and went on to make £3,000 profit. This was ploughed into the society by its president, who retired in 2007.

Further books followed including Round Tower Churches of South East England.

His research led him to the controversial conclusion that many more churches had been built by the Anglo-Saxons than previously credited. His books also sharply contradicted those historians who had claimed that the round towers were built as defensive watch towers.

Mr Goode went on to suggest that the design of round towers had been adopted partly because of the lack of dressed stones to provide quoins for the corners of walls.

And the skilled traditional builders, he contended – who would have used whatever material was to hand – would know how to use flint and lime mortar.

When the Normans and their successors also built or extend churches, it is likely that these local skills would have been used in parishes across East Anglia.

When he stepped down in 1992 as chairman after 19 years in post, he had visited all 181 round towers at least twice, and climbed every one except the ten that were unsafe.

By the second annual meeting, the membership of the society had grown from 24 to 70 and it received official charitable approval.

Five years later, the society's membership had reached 472.

In 2005, when the society's first study day was held at Mendlesham, near Stowmarket, it was announced that the Prince of Wales had agreed to become the society's patron.

The society, which has continued since the death of Mr Goode in 2008 aged 95, has continued his vision to maintain and safeguard the nation's precious heritage of round tower churches. On Mr Goode's death, Stephen Hart, a leading author and expert on church architecture, said that the society would remain a living memorial to its enthusiastic founder.