A favourite walk I take with the dog is the path along the trackbed of the old Witham to Maldon branch line.

Thanks to the Friends of the Flitch Way, the old platform is nicely preserved, and you can stand at the viewing point from which quite a few photographs were taken of trains stopping at the halt.

Looking at one such photo I had a sudden shock of recognition. It was a tiny, four-wheeled railbus, and I suddenly remembered an Airfix kit I had seen sixty years before.

A railbus is just that – a bus body on railway wheels. Unlike the multiple units we take into London, it is very light, with room for about fifty passengers, and also very economical to run. A steam train takes a lot of time and labour to prepare for operation, and in the 1950s they were very costly to run on small branch lines. The bigger DMUs (Diesel Multiple Units) which also ran on our line were better, but were far too big for the passenger traffic they attracted.

So railbuses might have been the salvation of small uneconomical branch lines, and that was certainly the logic behind British Railways ordering 22 railbuses from five different manufacturers in 1958 for trial on small branch lines.

Unfortunately, no single batch was larger than five vehicles, so the trial was half-hearted at best. Looking closer at it, my treasured Airfix kit was based on a batch of five made by Park Royal Vehicles. When Airfix marketed it in the early 60's they prided themselves on modelling cutting-edge technology. Some of this turned out to be a dead end.

Trialled on the Maldon, Saffron Walden, Braintree and Mildenhall branch lines they saved £66,000 in operating costs in their first year (about £1.5 million in today's money) but Beeching's infamous 1963 report on "The Reshaping of British Railways" paid little attention to the savings railbuses could bring, and the Maldon line was closed to passenger traffic in 1964.

The railbuses were stored and then sold off. Remarkably, in spite of question marks on their reliability, four still exist on heritage railways, with two regularly operating and two more (including the one at the East Anglian Railway Museum) under restoration.

Nor was this the end of the railbus saga. Second generation railbuses were produced from the mid-seventies jointly by Leyland and British Rail, and these led to the "Pacers" on which many of us will have had a bone-shaking ride.

There is a completely different story to be told about the German railbuses, which gives a tantalising glimpse of what might have been in Maldon.