BMW’s excellent new 3-Series range arrived earlier this year, and the brand has now expanded the line-up to include a new entry-level diesel, the 318d.

As with the previous car, the 318d gets a detuned version of the 320d’s 2.0-litre diesel engine, giving it 150hp rather than the 190hp of the most popular model in the range.

The 318d’s purpose, according to BMW, is to “capture drivers with a budget in mind”, costing just £10 more than the base petrol 320i model and £1300 less than the 320d.

It comes with the same SE, Sport and M Sport trim levels, and the main benefit is financial because, compared with the 320d, there’s just a 1g/km difference in emissions on the automatic, or 2g/km on the manual, which doesn’t make a difference to the benefit-in-kind bands.

But the ‘missing’ 40hp certainly makes a difference to the performance, with the 318d 1.3 seconds slower on the 0-62mph dash, at 8.4 seconds. It’s noticeable from the driver’s seat, with the 318d feeling somewhat lacklustre versus its more powerful sibling. It’s not terrible by any means, and that acceleration time places it neatly between equivalent Audi A4 and Mercedes C-Class rivals, but the comparison with the 320d isn’t favourable. Drive them back to back and the £1300 difference is well worth paying, especially when slightly better residuals on the more powerful model will narrow the price gap.

The auto gearbox fitted to our test car is a peach, but costs an additional £1550. At least that’s cheaper than the £1690 it’ll cost you on the 320d, the only other model offered with a manual. But it’s still a fairly big step, given that the 318d is the self-confessed budget choice. Despite that, only around 15% of buyers are expected to go for the manual where it is available.

The Sport trim of our test car is also an interesting experience. BMW has priced the trim levels temptingly close, and much like the step from 318d to 320d, and paying the extra £1500 to go from Sport to M Sport nets you the much more impressive 12.3-inch touchscreen (it’s also rotary dial-operated) with real-time traffic and connected services, as well as the M Sport styling package. It also adds the M Sport suspension, which makes the car feel sharper but more crashy over bumps. The Sport’s smaller steering wheel is also not as nice as the chunkier version you get in the M Sport.

Driven in isolation, there’s not a lot wrong with the 318d in SE or Sport trims. But if you’ve sampled the extra poke of the 320d, or those tempting M Sport extras, the lesser car is slightly tainted once you know what you’re missing.

The 320d M Sport is, for now at least, the dominant car in the range, and there’s a very good reason for that. It’s really very, very good – this new addition might be cheaper, but there’s a reason for that.

Paul Barker