New ferries also urgently needed to replace ageing fleet which is imposing "intolerable limitations"
The UK government should support and potentially help fund tunnels and bridges on shorter island crossings because of their "transformative potential", MPs have urged.
The conclusion of a Commons Scottish affairs committee inquiry published on Friday is likely to add further momentum to plans for new links in the Northern and Western Isles, such as a series of inter-island tunnels in Shetland.
They would be feasible over short distances at a time when ageing ferries are imposing "intolerable limitations" on communities, the committee concluded.
Shetland Islands Council gave the go-ahead last month to preparations for a £402 million, four-mile tunnel between Mainland and Yell.
It would be followed by another tunnel between Yell and Unst, with further tunnels or bridges to Bressay and Whalsay to come.
READ MORE: Drill and blast - how Shetland’s £1.5bn inter-island tunnel links will be built
The Scottish government, which is responsible for roads, welcomed the committee’s call for the UK government to play a “key role” in the delivery of such projects.
The committee said: “Given the scale, complexity and cost of fixed links projects, local authorities would struggle to deliver them alone and would benefit from UK government support.”
Its report stated: “The question is not whether the UK government can support fixed link projects in Scotland, but whether it is willing to do so.
“The UK government should actively engage with any proposals progressed by [island] communities and give serious consideration to the support it could offer them.
“However, in doing so, it must recognise that fixed links are unlikely to be viable on the basis of economic return alone.
“In assessing any potential support, the UK government should ensure that its appraisal of any projects fully captures the social and cultural benefits they could deliver, recognising that limited direct economic return on investment does not necessarily limit their worthiness.”
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The committee also said there was an urgent need to improve the ferry network since bridges and tunnels “would only ever be a viable solution on a handful of specific, shorter crossings, and the vast majority of islanders will continue to rely on ferry services”.
But it said fixed links “have the potential to deliver transformative benefits” on the basis of projects elsewhere such as in the Faroes, where 18 islands are linked.
It said: “When designed and implemented effectively, fixed links can help reverse depopulation trends, improve quality of life, and strengthen the economic prospects of fragile communities.”
A UK government spokesperson said: “Transport is a devolved responsibility, but the we support the growth of our island communities. We will respond to the Scottish Affairs Committee report in due course.”
A Scottish government spokesperson said: “We fully recognise the potential benefits fixed links could bring and welcome the committee’s conclusion that the UK Government has a key role to play in their delivery, alongside local authorities and the Scottish government.
“We have committed to working with local authorities to explore financing models.”
Shetland Islands Council leader Emma Macdonald said: "Shetland is leading the way in making Scotland a tunnelling nation.
“We now have a route map in place which, subject to funding, will deliver two subsea road tunnels and eight new inter-island ferries over the next decade."