It’s not over-egging it to say that the  Vauxhall Astra is probably the most important new model coming into the fleet market this year.

The UK’s number four biggest-selling fleet vehicle is also the most-registered for the UK’s number two fleet brand, which makes the new model a bit of a big deal.

BusinessCar will get to drive the car in September, so we won’t know exactly how big a step forward it is on the road until then, but on paper the difference is obvious.

Whereas before, the lower medium contender could only just scrape below 100g/km, Vauxhall has
jumped to the front of the class thanks to a headline emissions figure of just 82g/km for the 110hp 1.6 diesel, a number only Peugeot’s 308 can match among lower medium diesel rivals.

That, combined with Vauxhall’s fleet-orientated Tech Line trim level that gives satnav, an adjustable front arm rest and eight-inch colour touchscreen system, gives the Astra a major boost in terms of whole-life costs.

There have been significant price reductions on the major fleet trims too, in an attempt to boost appeal in the corporate sector, and one look at how the new Astra’s cost per mile stacks up against rivals shows how effective that has been.

In such a competitive segment, a 4p per mile advantage over the next-best in our basket of rivals is massive, and puts Vauxhall in a very commanding position.

Benefit-in-kind payments of £48 a month are £5 cheaper than the next-best for a lower-rate tax-payer, while the deprecation figure and SMR cost are both class leading.

The only places the Astra trails are in performance terms, where the 110hp diesel is the slowest to 60mph
by some distance of the cars here – a clear two seconds behind the next-slowest – and neither boot or fuel tank are particularly generous.

One word of warning on the new Astra: a little asterisk in the brochure points to the fact that the 16-inch alloys standard on Tech Line models, along with the entry Design trim, won’t actually be available until January 2016, so any early cars will come on steel wheels instead, and then be swapped onto alloys free
of charge when they become available. It’s also disappointing that Vauxhall’s new Onstar technology package won’t be standard on the Tech Line fleet trim, instead being a £395 option.

If the company wanted to get Onstar adopted quickly, then offering it with the fleet trim of its biggest-selling fleet model would have been a great place to start.

Read on to see how the Astra stacks up on whole-life cost against the varying strengths and talents of its Ford Focus, Peugeot 308, Seat Leon and Volkswagen Golf rivals.

Ford Focus

It’s a little ‘horses for courses’ with the Ford Focus, as there is a lower-emission Econetic model, but it only comes in entry Style trim.

That means to get anything that isn’t base spec, you need to go to a higher-emitting model, hence the 98g/km car analysed here that’s 9g/km behind any rival model in this basket bar the Golf.

The residual value is a big triumph for the Focus, beating all the others apart from the Golf, although top to bottom is covered by just 2.2 percentage points.

SMR costs are surprisingly high, putting the Focus fifth of five, £11 behind the fourth-placed Peugeot and nearly £250 off the Astra that heads this pack. A tiny boot – 54 litres off any of the others here – impacts practicality, and the Focus is also the heaviest car.

Seat Leon

Seat’s Leon is something of an underrated gem in the competitive lower medium volume segment.
Using parent Volkswagen Group technology, the Leon gets emissions below 90g/km, which puts it right in the middle of the two at 82g/km and the two just under 100g/km.

The Leon has the joint second-largest boot, although 90 litres behind the 308’s huge luggage area, and insurance costs are lower than all bar the Golf.

The depreciation figure is 0.02 percentage points better than the Peugeot, but if it were improved by one percentage point it would jump to second place of the five cars here, such are the small differences, rather than languishing in fourth place.

Peugeot 308

An impressive step-change from the last 308, the latest Peugeot model is the only diesel hatchback that can match the new Astra’s CO2 emission figures, although that is with a more powerful engine that, on paper at least, doesn’t compromise performance to the level the Vauxhall appears to.

In fact, the 308 is actually the fastest-accelerating car here, completing 0-62mph in  9.7secs, 0.8secs quicker than all bar the Astra, which is 2.8secs slower.

The 308 scores best of the five here for boot space and fuel tank range as well as the CO2 emissions, and also joins only the Astra in ducking under £20,000. The insurance group is, though, surprisingly high, and well above any of the others here.

Volkswagen Golf

Like the situation with the Ford listed above, this isn’t the most efficient version of the Volkswagen Golf, which is available in 89g/km Bluemotion low-emission specification, but only on a base trim level.

To get a higher level of kit, you need to step up to the Match model, which can only offer 99g/km of emissions, although the Bluemotion’s poor 30.9% RV, worse than any of the other four cars here, means it has a higher cost per mile than this regular Match model’s 33.8%.

It seems the used market isn’t so keen on these economy specials, and on total cost, the regular 99g/km car is 1.2p per mile cheaper to run than its more efficient sibling.

Otherwise, SMR and insurance costs are good, while BIK payments are high.