The acting couple, who presented the Channel 4 series Great Canal Journeys, are supporting an appeal for the reconstruction of the Schoolhouse Bridge near Pant, Oswestry.
The latest appeal by the Restore the Montgomery Canal team, has been made necessary by rising costs after the delays of Covid,
It will be boosted by an anonymous supporter who will match every £1 donated.
Timothy West and Prunella Scales are avid canal explorers.
Mr West said: "Sixty years after it was demolished we are tantalisingly close to reopening the bridge.
"This removes a huge obstruction to the Montgomery Canal restoration in England. It would be so good to see it reopen. With your help we can make it happen."
Schoolhouse Bridge, at Crickheath near Oswestry, is on last two miles of dry canal on the English side of the border and is the last highway blockage in Shropshire.
In Wales recently-announced UK Government grants will accelerate the reopening of the canal from the border to the isolated navigable section through Welshpool in Mid-Wales. The plan is that restoration will one day again connect mid-Wales to 2,700 miles of canals across England and Wales.
Michael Limbrey, Chairman of the Restore the Montgomery Canal group said, “The rebuilding of Schoolhouse Bridge will be one of the most exciting projects on the Montgomery Canal. We have to close a public road, dig out the 1960s embankment across the canal, construct a new arched bridge and then open the road again – all in a few months."
“Our volunteer team has worked hard over five years for the engineering and legal approvals. This has not been made any easier by the uncertainties and delays of the coronavirus pandemic. And now we are ready we find that the cost of everything is going up.
“Our appeal for Schoolhouse Bridge has had the most amazing support, raising over £500,000 with one-off gifts, monthly donations and added payments from companies and trusts. Now a generous supporter, wishing to remain anonymous, is offering to match every pound we raise up to £50,000. If you add the Gift Aid tax rebate of 25p for each £1, a £10 donation becomes £22.50 and a gift of £25 benefits the appeal by no less than £56.25.
“Schoolhouse Bridge is the main obstacle between Crickheath Basin - restored under a lottery project before lockdowns started - and the Welsh border at Llanymynech. As we could not see how the bridge could be rebuilt in the near future we decided to do it ourselves. Our volunteers prepared the design, the Canal & River Trust assisted with the planning permission and Shropshire Council has been most supportive in accommodating a project which must have been unlike any they had dealt with before.
“When the volunteers of the Shropshire Union Canal Society reach Crickheath Basin – hopefully later this year – there will just be two miles of derelict canal to Llanymynech and we are working with Shropshire Council to gather all the information needed to fund the restoration of that section.
“After interruptions of the last year or two, we now have to finish raising those funds for the bridge. Donations are already coming in and we shall be delighted to receive more through our Local Giving page https://localgiving.org/charity/restorethemontgomerycanal.”