There was something strangely prophetic when ERF, then one of Britain's few remaining independent truck manufacturers, struck a deal with another small truck maker, Steyr of Austria, to supply cabs for its medium truck range back in the late 1980s. First Steyr was acquired by MAN in the early 1990s, and then just a couple of years ago, the Bavarian company added ERF to its portfolio too.

ERF buyers, who previously had the choice of the company's full-sized GRP cab or the Steyr cab for middleweight rigids, now have an updated choice. The revised Steyr cab is still on the menu, shared with MAN light and middleweight models. ERF cab production didn't survive the MAN take-over so those who want the space of a larger cab can pick MAN's long running M2000 cab, a variant of which graced all the company's heavy range before the TGA series was launched. Long in the tooth it may be, but since the old MAN cab was always one of the better places to spend a driving day, isn't necessarily a problem. Or is it? We took to the roads in an 18-tonne ECM to find out for ourselves.

Both the Steyr-cabbed ECL and ECM rigid ranges are available with a wide range of chassis including 4x2, 6x2 rear lift, 6x2 rear steer, as well as 6x4 and 8x4 for tipper use. Effectively, the ERF range mirrors the MAN M2000 in its choice of cabs. Both variants are available with day or sleeper cabs but the ECM models include a number of refinements as standard, as well as more space in the cab. Among these are a four-bag air-suspended drive axle, cruise control, air-suspended driver's seat, electric windows, central locking, heated driver's seat, electrically heated and adjustable door mirrors and a cab heater. From a driver's perspective, this means there are a few creature comforts taken for granted that might appear on the extras list from some rivals. While the sleeper cab version, on test here, hardly counts as one of the most spacious, bear in mind that we're talking about a standard roof sleeper, intended for occasional nights away, not an intercontinental mile-cruncher.

Any driver familiar with MAN's 1990s M series cab will feel instantly at home behind the big steering wheel. Dash panel, switchgear and controls, not to mention the cab itself are all as they were back then. Where the ERF scores is in the choice of engines. At the nominal 220bhp rating, buyers can pick either the seven-litre MAN engine, or six-litre Cummins ISBe. The principal difference can be nailed down to marginally more torque from the MAN motor. 627lbft (850Nm) plays 605lbft (820Nm) from the Cummins over roughly the same revband. MAN claims a spread of 1,200 -1,800rpm at maximum torque, while Cummins reckons 1,200 – 1,700rpm. Against that, the MAN engine predictably weighs more, adding 90kg to the chassis unladen weight. If weight is crucial, the Cummins engine has the edge.

Both engines drive through a ZF six-speed synchromesh gearbox, while MAN-powered models have the option of an Eaton nine-speed synchromesh, although I can't believe that ERF wouldn't offer the nine-speed box to Cummins customers if they demanded it. The Eaton box adds a further 60kg to the weight, though. Although developed from the earlier Cummins B-series engine of the same capacity, the ISBe has grown out of the European Engine Alliance joint venture with Iveco and Case New Holland (an Iveco subsidiary), so anoraks can spot the same engine sporting Iveco codes in EuroCargo chassis, not to mention the DAF LF too.

The first thing that really impresses with the ISBe engine installed under the MAN cab floor is the lack of noise. We have common rail injection to thank for that, using pilot injection – a small quantity of fuel injected just before main injection takes place, to soften the diesel big bang. The result is a smooth engine, with cab noise levels to rival those of a big artic. Even towards the top of the rev range, the engine never sounds or feels frantic. But like most diesels, there's a point beyond which nothing much else happens. For the ISBe, this is around 2,000rpm. It may develop maximum power at 2,500rpm, but in practice, topping 2,000rpm achieves little, unless you're slogging up hills, even though the green economy band stretches from 1,200 to 2,200rpm.

It's at the other end of the rev range that the engine shows its mettle. No B-series would have been happy to lug down to around 1,200rpm. You would be grabbing a downshift long before then on a hill, but the ISBe will happily go on pulling all the way down. It still appreciates higher revs on a steep slope, but on the level, it pulls cleanly from low down.

A few years ago 12/13mpg would have been a good average result from a fully laden 17-tonner, so to average some 14.6mpg from an18-tonner around our test route rising to 17.7mpg over the M4/M5 motorway section is a fine result. The ZF six-speed synchro box is light and precise to use, even if the throw seems unnecessarily long. The clutch is reasonably light too, so in-town work shouldn't be too hard on left knees. Even so, hills offer plenty of left leg exercise. The ISBe is fitted with an exhaust brake as standard and like most such devices, it is only effective at high revs, particular on a relatively small engine. A blue sector on the rev counter indicates the most effective range, spanning 1,800 – 2,900rpm. The exhauster is activated by a heel button operated by your left foot. So getting the best out of it involves a down-change, then heel pressure to close the exhauster butterfly valve, holding it there for as long as it's needed. More drivers might be tempted to use it if the switch were moved up to the steering column, following modern practice, preferably with an automatic and manual setting.

Otherwise there is little to fault from the driver's perspective. The steering column is reach- and rake-adjustable, the air suspended seat smoothes out all but the worst of the bumps and there's plenty of adjustment to suit all shapes and sizes. Consider the other convenience features like the standard night heater, electrically adjustable mirrors and central locking and the ECM doesn't disappoint.

The old MAN instrument panel provides clear concise information, with dials flanking a bank of central warning lights. There's just one column stalk, Mercedes style. It would be better if wiper and light functions were split across two stalks for simplicity and the cruise control integrated with the exhaust brake in another stalk. Otherwise the layout has stood the test of time well. The sleeper cab offers a number of advantages other than the single bunk. Beneath it is a cavernous storage space, split into three, providing a capacious centre compartment flanked by two smaller spaces. The bunk can be hooked up to improve access. An external locker each side provides space for gloves, ropes and tools. There's also a large lidded compartment over the engine cover that will hold dockets, pens, clipboards and plenty more besides, without impeding cross cab access. Then over the windscreen, three more storage compartments provide yet more space. All in all, it's not bad for a low-roof cab.

It's a tough market out there, as any truck manufacturer will tell you. The ERF is up against more modern competition such as the Iveco EuroCargo, DAF CF and just revised Mercedes-Benz Axor, not to mention the latest Scania P-Class, Volvo FM and in-house competition from MAN's M2000 range – effectively the same again without the Cummins engines.

While it's hard to ignore the more modern interiors of many rivals, the cab comfort and low noise levels from the Cummins ISBe show that there is plenty of life left in the ECM yet. Add in the easy driving experience and fine fuel consumption and there isn't a lot to fault in this particular blend of German, British and American truck engineering.