THE bus seems to be straining every muscle and sinew in its ageing but resilient red body.

A seven-litre diesel engine, made by the Gardner company long before Cummins and other high technology manufacturers grabbed a big slice of the market, rumbles and grumbles beneath a gently vibrating bonnet.

Unidentified things shake and rattle and occasionally you think you can even detect a bit of a roll, especially when you are sitting on the top deck with a panoramic view of other people's gardens, whether they be a work of art or a wilderness.

Tackling a steep hill from a standing start can be a daunting business when all you have is an old-fashioned four-speed crash gearbox and the most you can muster on the level, with a following wind, is about 38mph.

One such demanding incline at Scotton, just outside Catterick Garrison, catches us on the hop and our gallant driver John Banks, squashed into a tiny cubbyhole of a cab, has to take another run at it before we surmount the summit.

But then this restored bus is 60 years old, after all, built not for speed but for carrying bodies from A to B. And it is only when you travel on GHN 189 that you realise how noisy, slow and stately buses used to be, given the hindsight and comparisons bestowed by modern air conditioning, revolutionary designs and more powerful engines.

What character GHN 189 possesses, though, in an age when visually most buses seem to emerge from the same jelly mould.

GHN 189, a Bristol K5G registered in August 1942, is a surviving representative of United Automobile Services, that leviathan among British bus companies whose sphere of influence once stretched from Northumberland to North Yorkshire and even touched Carlisle.

United is now but a memory, its name having been obliterated and its operations taken over by the omnipotent, international Arriva. Compared with Arriva, United now seems like a minnow in a big pond.

But United has its supporters and the United Enthusiasts' Club is dedicated to perpetuating the memory of the old firm from Grange Road, Darlington, where a Safeway supermarket now stands. Today the club has collaborated with the Aycliffe and District Bus Preservation Society, owners of GHN 189 since 1981, to help the veteran celebrate its 60th birthday year by retracing some of its original wartime routes in the Richmond and Catterick areas.

Nowadays GHN 189, with a body built by Eastern Coachworks of Lowestoft, Suffolk, is best known as one of the Heartbeat buses, but that claim to fame came late in its life, as it does to many character actors.

United itself was only 30 years old when GHN 189, one of 4,141 Bristol Ks built between 1937 and 1957, first turned those big black wheels. Based for the first few years of its life at the United depot in Richmond, it then plodded patiently along various highways and byways without any recognition at all until it was sold to a South Wales company in 1959.

They got rid of it in 1969 and a year later it was reclaimed for preservation by the Rev Philip Battersby, of Middlesbrough, who today is sharing the driving duties with Mr Banks, from Stockport, a fellow officer of the United club.

Saturday market shoppers turn their heads as we grind out of Feethams, Darlington, threading our way among blue Arriva buses and others with the extravagant rainbow stripes of Stagecoach, towards Stapleton, Barton and the old haunts of GHN 189.

Richmond Town Pipes and Drums are belting out Amazing Grace as we lumber on to the cobbles in Richmond and it is fancifully conjectured that they constitute a welcoming party. "They must have known we were coming,'' someone jokes.

Away from that draughty open rear platform, the top deck evokes random childhood memories. Each of the four rows of bench seats has a shiny metal protuberance on the back called a stubber, for extinguishing cigarettes or striking matches on in the days when smoking was allowed on buses, and an oval label exhorting passengers to mind their heads when leaving their seats.

It is pure joy for people like retired bank manager Mike Harper-Tarr, who used to live in Guisborough and has travelled from Banbury, Oxfordshire, for the trip.

Mr Harper-Tarr, a member of the Omnibus Society, says: "I worked and drove all around here but never had a view like this, and these seats are more comfortable than some modern ones.''

Two of the oldest passengers are 68-year-olds Don Roberts, from Redcar, and Howard Dunn, of Middlesbrough, who were United parcel boys at Middlesbrough bus station in 1949.

Mr Roberts says: "Modern buses are just like boxes on wheels. This one has character, just like a steam train.''

Mr Dunn, who also drove buses for the old Middlesbrough Corporation for four years, recalls: "In those days you could tell by the noise of the engine which make of bus was coming.''

The United Enthusiasts' Club finds its newest potential member in 12-year-old Dean Storey who, with permission from his parents on a Richmond market stall, is allowed to hitch a lift on GHN 189 to Catterick Village and back. Bus enthusiast Dean, who lives in Darlington and collects exact scale model replicas, says later: ''It was a good journey but very slow and the driver had to have another go at one of the steep hills.''

GHN 189 shows its mechanical mettle on the way back to Darlington. Wry smiles break out on board and cameras are produced as we approach an Arriva bus, a mere ten years old and probably capable of twice our speed, which has broken down on the slip road leading off the A1 at Barton. A helping hand is offered but it seems a replacement bus is on its way to pick up the handful of passengers. GHN 189 trudges on and completes its 59-mile journey into the past almost exactly on time.

Age and experience count. That's what they call survival. And the atmosphere has been such that the D&S Times really feels it has been among friends.

* Aycliffe District Bus Preservation Society, which was founded in 1980 and leases premises on Aycliffe industrial estate, is a registered charity and a small museum provisionally registered with the Museums and Galleries Commission.

As well as GHN 189 it owns and has restored two other former United buses, both single deckers dating from 1949 and 1969, and a 1964 Darlington Corporation double decker.

It is halfway through restoring a 1958 United long distance coach, towards which national lottery funding has been received. Members meet on Tuesday evenings and on Sundays. Enquiries to Ian Wiggett on 01325 317657 or John Gibson on 01325 312656