At the start of 2021 and the implementation of Brexit, a trade border was created between Great Britain and Northern Ireland. What does this mean for ordinary people who cross the Irish Sea? And where exactly is this border anyway? Neil McCarthy boards Stena Line's ferry 'Embla" which plies a daily and nightly course between Birkenhead and Belfast. He talks to passengers, and crew, lorry drivers and historians, crossing this body of water that both separates and binds the two islands on a search for the elusive line in the water. 'Meridians' written and read by Mark Ward Sound design by Phil Channell Produced and presented by Neil McCarthy