When I first started exploring the county of Suffolk ten years ago, it was in the company of dead men. The best of these men, Munro Cautley, had travelled the same pathways as me a quarter of a century before I was even born, but still I found his help invaluable. His post-war Suffolk Churches and their Treasures was still regarded as the definitive guide to the county's churches. There was also Nikolaus Pevsner, whose Buildings of England series is rightly seen as one of the great literary achievements of the 20th Century. But Pevsner had been ill-served in Suffolk: the 1975 revision of his Suffolk volume was perfunctory at best, and, apart from noting the extensive redevelopment of Ipswich, is little different to the 1961 original. Arthur Mee was amusing, but his The Kings England: Suffolk had been published before the Second World War, and since then the county had undergone radical changes. These dead men were pleasant company, but again and again I tipped up in remote parishes to find the church converted into a house, or surrounded by excrutiating suburbia, or even completely vanished. It was like using a map which was half a century out of date. And then I discovered DP 'Sam' Mortlock. In the late 1970s and 1980s, he had cut a three volume swathe through the churches of Norfolk in the company of Charles Roberts, and he had then proceeded to do the same for Suffolk, this time on his own. The six volume Popular Guide series was an anti-clockwise tour through the two counties, and it got better as it went along. Mortlock and Roberts had started in Norwich and north-east Norfolk, replicating the area covered by the first of the two Pevsner volumes for Norfolk, describing the churches in brief details. But then they got into their stride, and it had taken them two volumes to visit the area covered by the second volume, and fully three for Mortlock to explore the county of Suffolk, which Pevsner managed in a single, much smaller volume. And Mortlock was just exploring the churches, of course.

Discovering Mortlock was a little like putting the lights on. The three Suffolk guides, now updated and brought together in a single lavish 600-page volume by Lutterworth, were originally published by Acorn Press, a small Cambridge-based publishing house, and by the early years of the 21st Century they were difficult to obtain, and still apparently little-known. The books are organised alphabetically by parish name, each entry being a methodical guide to the exterior and then the interior of the parish church. Mortlock had originally explored Suffolk in three vertical strips, covering the Western, Central and Eastern parts of the county. What a joy it is to have them republished together, in a single alphabetical sequence, extensively revised and updated.

The beauty of Sam Mortlock is that he writes as an enthusiast. While there is no doubt about his expertise, or the completeness of each review, he is never formulaic; his eloquent prose finds room for insignificant details which he happens to find interesting, alongside the expected naming of furnishings and architectural features. Coming to a known church with Mortlock is like seeing it for the first time. Secondly, the articles are largely accurate; you know you are in the presence of a learned man who has walked these ways before you. Most importantly of all, Mortlock has what I think of as an Anglican sensibility. He knows the true emotional value of the buildings he describes. These three aspects of his work mean that he is a more affable, knowledgeable and enjoyable companion than Pevsner.

Compared with Norfolk, the entries in Suffolk are often lengthy, running perhaps to several pages for even some of the lesser-known churches. A typical Mortlock description of a church begins with a tour of the outside. He has the engaging manner of a detective, piecing together the story of the building from the available evidence, describing the historical development and any idiosyncratic features. Once inside, his eye ranges around the fixtures and fittings, their age, provenance and significance. He has a particular knowledge of post-Reformation memorials and 19th century glass, making him a useful counterpoint to Cautley, who paid full attention to medieval features, but usually ignored the rest. In almost every church Mortlock finds something which you would not otherwise notice. He muses on inscriptions, sometimes allowing himself a quiet chuckle and inviting us to join in. And yet, he never loses the discipline of the investigator, and rarely misses anything.

Mortlock is a handy companion to any visit, but I like him better to come home to, when I can read and understand what I've seen, and what I've missed - oh, the pleasure of knowing that there needs to be a second visit! Best of all, his book is to be read idly and at leisure, for compiling a wish-list of visits, and making mental notes about things I'd really like to see. Even though I've now visited every Suffolk parish church, I still do this. It is a form of church exploration in itself.

The old Suffolk volumes were always better than the Norfolk ones, and the new Guide to Suffolk Churches is outstanding, even better than the revised volume for Norfolk. This is partly because the revision and updating has been much more rigorous than it was for Norfolk. Special attention has been paid to updating events since the 1989-92 publication of the volumes of the first edition, and the local Anglican Diocese has been extremely helpful, allowing access to faculties for extensions and refurbishments, and particularly to details of millennium projects, many of which were in stained glass. Sam spent more than a year revisiting many of these in person. Because of this, there is not much missing. All that seems to have fallen through the gap between the two editions is a handful of minor projects completed before the new millennium - of these, probably only the omission of Surinder Warboys' fabulous 1990s windows at Chillesford will raise the eyebrow of any future explorer.

Unlike the volumes for Norfolk, the first Suffolk books also contained the modern churches as well, however insiginficantly they might have been tucked away in the suburbs of Ipswich or Lowestoft. They are a feature of the new edition too, and, ironically, this causes a slight skew of emphasis, not least because you will not find any of Suffolk's dozen or so outstanding earlier non-conformist or Catholic churches here - Sam is rigorously Anglican in his tastes. However, as a bonus, that great Suffolk bell-ringing expert George Pipe, a friend of Mr Morlock for many years, has contributed details of all the ringable bells in the county.

Sam is now in his mid-eighties, and although he looks a good twenty years younger, he tells me that the Norfolk and Suffolk volumes are his 'swansong'. Although I think there is plenty more to come from the pen of Mr Mortlock - he is writing a history of the Earl of Leicester's library, and there are also rumours of a book about almshouses - there is no doubt that these two volumes will be his great legacy. I said in my review of the Norfolk volume that it was essential reading. I think that the Suffolk volume is more important than that. In the absence of any proper revision of the 1961 Pevsner, it remains the only complete and reliable guide to the churches of Suffolk in print. Even when Pevsner's revising editor has completed his work, I believe that Mortlock's Guide to Suffolk Churches will remain the definitive text on the subject for a half a century or more to come.