The president of the Supreme Court has called on the Government to provide greater clarity over the role of the European Court of Justice after Brexit.
Lord Neuberger said it would be "unfair" to blame judges for making the law "when Parliament has failed to do so".
Ministers have made clear that the top European court's jurisdiction will end after the UK leaves the European Union.
But they have also said that UK courts should continue to interpret European Court of Justice (ECJ) case law around legislation derived from the European Union, on issues such as workers' rights.
Lord Neuberger, who stands down as Supreme Court president next month, told the BBC: "If (the Government) doesn't express clearly what the judges should do about decisions of the ECJ after Brexit, or indeed any other topic after Brexit, then the judges will simply have to do their best.
"But to blame the judges for making the law when parliament has failed to do so would be unfair," he added.
The Government's Repeal Bill says no UK court will need to have regard to decisions of the ECJ post-Brexit, but may do so if it considers it appropriate.
Lord Neuberger said all judges "would hope and expect Parliament to spell out how the judges would approach that sort of issue after Brexit, and to spell it out in a statute".
He said he was more concerned about rulings the ECJ made after Brexit, adding: "If the UK Parliament says we should take into account decisions of the ECJ then we will do so.
"If it says we shouldn't then we won't. Basically we will do what the statute says."
A government spokesman said: "We have been clear that as we leave the EU, the direct jurisdiction of the European Court of Justice in the UK must come to an end.
"However, we want to provide maximum certainty so the Repeal Bill will ensure that for future cases, UK courts continue to interpret EU-derived law using the Court of Justice of the European Union's case law, as it exists on the day we leave the EU."