Is this the line that goes over the Merseyrail electric line south of Seaforth and Litherland station then runs parallel to the line, but behind the railway stations at Bootle New Strand and Bootle Oriel Road. If so, what use would Network Rail make of it?
You can get onto it via a junction to the Bootle-Edge Hill line. It's not owned by Merseyrail AFAIK. It's a few years since I've visited the area so I don't know what state it's in or if any trains have used it recently.
By the way Spain seems to abound in long stretches of rusty track that haven't seen a train in years.