Historian Simon Schama and TV presenter Natasha Kaplinsky addressed the launch in Parliament of a project to map and preserve historic European synagogues.
Commissioned by the Foundation for Jewish Heritage, the project inventories 3,318 synagogues in 48 countries across Europe.
The buildings have been catalogued on artistic, urban and historical significance. The foundation has highlighted 160 it believes require urgent attention and the Merthyr Tydfil and Sunderland shul buildings are among them.
Mr Schama said it might reasonably be asked that in areas now without Jewish population, because of extermination or assimilation, "why should we bother? The answer is that the present is, in the chain of memories, about human vitality, the vitality of communities.
"So if you do this, you bring back not only Jewish memory, you bring back what Europe was. Europe had Jewish life as much as it had Christian life so we are in a sense validating the entirety of our historical memory.”
Ms Kaplinsky spoke about her paternal family’s links with Slonim in Belarus and its Great Synagogue, one of those in the "at risk" category.
The Kaplinsky family is interested in helping to restore the 17th century building for use as a Jewish museum, educational centre and cultural venue – as well as reviving it as a place of worship.
“Slonim had 17,000 Jews prior to the Second World War. By the end it was estimated there were 200. Slonim isn’t just an old synagogue in need of a bit of TLC and repair. It is a lasting testament to a destroyed community.”
Dame Helen Hyde spoke about other synagogues the foundation has begun to focus on.
In Merthyr Tydfil, conversations instigated by the foundation have resulted in a feasibility study to explore plans to restore the building as a museum of Welsh Jewry.
In Sunderland, the foundation is working with the Churches Conservation Trust to identify possible future uses for the site.
Michael Mail, the foundation founder and chief executive, said the time had come for action.
“This is not just Jewish heritage, it is Europe’s cultural and historical heritage and we are in a race against time to save it.”
Other supporters of the project include Downton Abbey creator Lord Julian Fellowes, authors Linda Grant and Howard Jacobson, architect Daniel Libeskind, sculptor Sir Anish Kapoor and journalist and broadcaster Robert Peston.
In September, the foundation is hosting a conference – Urban Jewish Heritage: Presence and Absence - in the World Heritage City of Krakow, Poland.