Plans for a multi-million pound Tube extension are back in court on Wednesday after 18 months of legal wrangling.
Inside the goods yard is the historic Braithwaite Viaduct
London Underground (LU) plans to extend the East London Line to Highbury in the north, West Croydon in the south and west to Clapham Junction to create an "M25" on the network.
But the plans hit the buffers when a railway enthusiast appealed to the High Court because they involve demolishing part of the Bishopsgate Goods Yard.
The yard houses one of the world's earliest surviving railway structures, the Braithwaite Viaduct, built in 1839.
In May the court ruled the demolition of part of the goods yard could go ahead once conditions to protect the viaduct were in place.
That decision is being challenged by local railway enthusiasts who want to protect the goods yards at the Court of Appeal on Wednesday.
LU says the extension will mean billions of pounds of regeneration for east London and insists it could still be completed before the end of the decade.
But a spokesman said: "If further unnecessary delay is experienced it is possible that the project could be lost."
The Court of Appeal is expected to sit for three days and a decision is due shortly afterwards.