More than 50 people have died on the A5 since 2006 and campaigners have called for the road to be upgraded.

The road is the Northern Ireland part of the major arterial route that connects the north-west of the island – Donegal and Londonderry – to Dublin, via towns including Strabane, Omagh and Aughnacloy.

The dual carriageway scheme was first announced back in 2007, but has been beset by a number of delays.

The 58-mile (94km) £1.7bn project was given the green light by Stormont ministers in October last year.

Speaking to BBC’s Good Morning Ulster programme Mr McClenaghan said “land was taken away” from farmers last October.

“The level of compensation has not yet even been determined and farmers have been reluctant to accept offers which may have been made because they don’t know what the final costs will be.

“Our feeling is that if our farmers are to be displaced they should be fairly compensated.

“Twenty years this has been going on and the important thing is that the A5 is safer for all the people that use it. We need to get on with improving the A5 road and we do not disagree with that.”

He said 330 farmers were affected.

“This is their home,” he said.

“There’s an attachment on the land that goes past any value or compensation amount and there are other farmers that want to get on with their business.”

Stephen Kelly from Manufacturing NI said the road was a critical piece of economic infrastructure and a critical piece of safety infrastructure for people.

His father Terry was killed instantly when the van he was a passenger in left the road at Bready, on the stretch of the A5 between Strabane and Derry.

Mr Kelly said he was disappointed by the decision, which he described as the latest episode in the “disaster” for the department.

He said the judge’s comment that the delay would coincide with more loss of life was “chilling”.

“Obviously, the judge is trying to make clear there was a strong moral case for this to be done,” he added.

“He did leave the door open, he said the department needs to go back and do more homework, provide more information, a better plan.

“The judge is really clear, this road is essential and needs to be built.”

Deborah Erskine, chair of Stormont’s Infrastructure Committee, said there were worries over how new road projects would be delivered.

“We are going to have to look at climate change legislation. It has huge implications for major road infrastructure projects across Northern Ireland,” she said.

She added there were “major questions” for the Department for Infrastructure.

She said: “Why was land ripped up and made unrecognisable while a High Court judgement was under way? And when will these farmers receive this land back?”

The High Court judgement blocking the upgrade of the A5 road – because the plans did not comply with government climate change targets – shows the reach and impact of Stormont’s climate change legislation – but the judgement is clear that shortcomings in the project can be remedied.

A solicitor for the Alternative A5 Alliance campaign group, which brought the successful case, said his clients’ efforts had been “vindicated” and it was an important day for the environment.

Safety campaigners from the Enough is Enough group said they were disappointed with the decision but added the judgement provided a “roadmap” for how the upgrade could proceed.

On Tuesday, the organisation Friends of the Earth welcomed the judgement and said “money earmarked for the A5 project should now be redirected to meet other challenges in Northern Ireland’s climate change legislation”.

The Irish Minister of State Charlie McConalogue, who is a TD for Donegal, said the decision was “extremely disappointing” and added transport access to the north west is “vital” and work “must now commence” to get the “go-ahead” for A5 work.

Kieran Kennedy, chair of Strabane business improvement district group, said Monday’s judgement was a shock.

“We in the north west depend on infrastructure to carry goods along the A5 corridor… this is just a severe blow to business in Strabane and the north west in general,” he told BBC Radio Foyle’s North West Today programme.

“I think about the families who have lost loved ones. There are obviously going to be more families affected in the future by this judgement.”

Mr Kennedy said it was a setback but “not the end”.