As the focus on emissions continues and the Government  ramps up vehicle taxation across the board, you need to make sure that your fleet is as efficient as possible. It's not just about saving the planet - how green your vehicles are has a severe economic impact aside from and above any social, moral or corporate responsibility considerations.

That's why BusinessCar has undertaken some in-depth analysis of the various elements that show how eco-friendly each of the UK's top 20 manufacturers, by 2014 fleet registration figures, are, as well as how quickly they are moving in the right direction.

The Society of Motor Manufacturers and Traders has again delved into the huge catalogue of data it has available to help us out with four of the 10 categories on which we assess the manufacturers. It has provided the average fleet registration emissions figure for each brand, from which we can also calculate the percentage change on last year to see how quickly manufacturers are cutting their CO2 emissions, or not as is the case with two brands this year.

The SMMT has also provided us with the same figure for fleet registration of each company's biggest-selling fleet model, and again we've awarded marks based on how much that has dropped, and also how it compares with the sector's average fleet emissions figure.

We've also taken an international angle, digging out each marque's individual EU target, which is calculated using vehicle mass set against CO2 to avoid unduly penalising those that sell larger and heavier vehicles. Manufacturers need to meet these targets to sidestep fines, and while 18 of the 20 are below their figure, we've awarded marks based on how far under they have fallen.

Then, with the help of BusinessCar's online CO2 calculator, provided by ComCar, we've looked at the two categories at the bottom end of the company car benefit-in-kind scale, and what sort of product offering each brand has below 76g/km and 95g/km to help those looking to minimise BIK bills and operate the most efficient fleet.

From there, the CO2 calculator has also provided the data on each manufacturer's lower medium
model - the heartland of the fleet sector - and how they compare with each other.

Finally, we've looked at the all-round current and future green efforts of each brand, and graded according to how much of a complete range of offerings the company has for those looking for the greenest solutions, both with the current range and with what will be arriving over the next couple of years.
Each category is marked out of five to give an overall score out of 50, which we have doubled to give a nice, round percentage result.

Toyota has come out on top in five of the previous seven years we have carried out this analysis, punctuated only by victories for Peugeot in 2012 and Renault last year. But, as you'll see below, we have a new name at the top this year. Read on to see why, and find out where the other 19 brands have found themselves in 2015.

1. Volvo - 86%

Volvo's continued improvement and introduction of lower-emission engines has seen it take a well-deserved victory and commendation as BusinessCar's greenest brand.

It's a far cry from the first survey seven years ago when the company placed at 15 out of 20, and the improvement is a reflection of Volvo's investment in low-emission diesel and plug-in hybrid technology under Chinese ownership.

Adding two new plug-ins per year until 2020, along with replacements for the older models such as the V70 and S80, should help keep the momentum of improvement intact.

2. Toyota - 84%

A winner in five of the seven previous analyses, the Japanese hybrid expert has gone mighty close to another victory this year, missing out by the smallest of margins thanks to remarkable consistency across all our categories of assessment.

A bit more evidence of future developments to continue the high standards of low emissions could have been enough to drag it up to, and maybe even past, Volvo at the top of the table.

3. Peugeot - 82%

Peugeot drops one place on last year to round out the 2015 podium, having scored maximum points in six of the 10 categories.

Only a minimal reduction in CO2 for its biggest fleet seller, the 208, and a solitary model available below 76g/km proved costly, but the revised 208 should provide another step-change in the next couple of months.

Peugeot was also only in the middle of the pack in terms of how quickly its average fleet emissions fell last year.

4. Renault - 80%.  Lowest average fleet emissions

Just six percentage points covered the top four brands, and it's last year's number one Renault that is at the tail end of that procession. A lack of evidence of future emissions-reducing introductions was the most costly issue, although when details of the new Megane begin to emerge then that may make a difference.

That would also help the French brand's score in the lower medium sector, where the Megane's 90g/km is now bettered by much of the industry.

5. Citroen - 77%

A previous high-flyer, Citroen still has plenty of strengths but suffers from having just one car below 76g/km and the fact that the C4 Picasso (pictured), Citroen's number one in fleet, recorded the same average emissions as in 2013. Credit, however, for the big year-on-year CO2 reduction.

6. Nissan - 76%. Most improved

The new Qashqai (pictured) has proved to be the catalyst for Nissan's jump up the table, producing a huge 19.5% cut in the model's average fleet emissions compared with the previous car. That helped the brand's overall CO2 drop, which was the most of any here, aided by the new Pulsar lower medium hatch.

7. Volkswagen - 70%

A surprisingly mixed bag from a company rapidly launching into the plug-in arena, with two more models set to join the two already on sale. A tiny 0.8% cut on 2013 average fleet emissions and a year-on-year CO2 increase for the Golf were the problem areas, but there's plenty of good stuff on the way.

8. Mercedes-Benz - 68%. Most models below 76g/km

Proof that big premium brands can still offer low-CO2, Mercedes' moves into plug-in and hybrid technology have provided a range of low-emission alternatives, and continued diesel development has given the brand a healthy decrease on 2013's average fleet emissions.

9. Ford - 58%

Ford heads a gaggle of four firms separated by just four percentage points around the middle of the table, offering a good range of models under 95g/km, but recording a comparatively small percentage drop on 2013's fleet figure. A brand with plenty around the middle of the sector, but little leading it.

10. BMW - 57%

BMW's average fleet emissions levelled off at a fairly high point last year, although the 3-series enjoyed a decent 2.5% fall and the i3 and i8 plug-in models scored the brand some useful points. It will be interesting to monitor where BMW's electric strategy, both with the 'i' brand and in the mainstream models, takes it.