Land Rover has already moved to a Euro5-compliant 2.2-litre diesel.Land Rover will show an all-new Defender concept at next month's Frankfurt Motor Show, pointing to a possible new addition to the range.
The off-road specialist makes the Defender 90, longer-wheelbase 110, and even longer 130, in hard top, pick-up, station wagon, cab chassis, and double cab guises.
But pre-show talk has it that an all-new pick-up to rival workhorses like the Toyota Hilux and Nissan Navara will be spun off the concept when the next-generation Defender goes into production in 2015.
Land Rover wants to break into new global markets with the mud-plugger as it expands its model range, one of which is the Range Rover Evoque, on sale in New Zealand in November.
The Defender concept has been designed to sell in the United States, where the current model falls foul of design laws, unlike the Discovery, Range Rover and Freelander.
The concept comes only months after Land Rover admitted that finding a replacement model for the Defender was a "huge challenge".
Land Rover managing director Colin Green said: "If we get it wrong we are messing up one of the industry's biggest icons, and in that sense it's a tremendous responsibility."
Green said the issue was how to keep the Defender's legendary capability, but expand its appeal to attract new customers seeking a less-functional vehicle.
One proposal would see a new version built on the same platform as Discovery and Range Rover Sport, but that chassis is relatively expensive.
Other options include fitting cleaner engines to extend the life of the Defender yet again, or a complete redesign, said Green.
"Another option is to carry on the current model using Euro6 engines," he said.
"A third is that we abandon that section of the market.
"It's our least preferred choice because we have serviced that customer base for a long time, but there's no point in servicing the customer and not the business.
"We have to make money and all three options are on the table."
The company has moved on one option by replacing the 2.4-litre turbodiesel unit from the Transit van with a Euro5-compliant 2.2-litre oil-burner.
The larger displacement Euro4 2.4-litre appeared under the bonnet of the Defender in 2007 when Land Rover improved the suspension and gearbox and changed the interior seating.
The new 2.2-litre engine produces the same power and torque (90kW/360Nm) but the smaller displacement uses less fuel and delivers lower CO2 emissions - 266g/km for the Defender 90 and 295g/km for the 110 and 130 variants.
The six-speed transmission has been retained but the air-conditioning is more robust, mostly to cope with the more extreme temperatures in which Defenders often operate.
"The substantial improvements to the Defender in 2007 transformed its on-road refinement and comfort while extending its capability off-road," said John Edwards, global brand director.
"With the introduction of the new 2.2-litre diesel engine and two optional suspension packs, the Defender for 2012 now offers greater customer choice than ever before."