The Labour leader has said approval should not be given for a new oil and gas development west of Shetland.
The Cambo field is waiting for final consent from the regulator, the Oil and Gas Authority.
On a visit to Scotland, Sir Keir Starmer said that as the world prepares for the COP26 climate change summit, the oil field should not go into production.
He also Prime Minister Boris Johnson of being “hopeless on substance” for saying he was not aware of the issue as he began his own visit to Scotland on Wednesday.
On Thursday, Mr Johnson said contracts should not be “ripped up” – but that we need to transition to renewable energy sources “as fast as we reasonably can”.