The U.K. currency spiked against the dollar on Thursday morning after the country's High Court ruling that any proposed Brexit plan would have to be approved by lawmakers before being implemented.

The pound rose close to 1.245 against the greenback, after starting the session at 1.230, although it quickly fell back to trade at around 1.240 at 10:20 a.m. London time. At one stage the currency was up 1 percent for the session.

The court ruled that the entire U.K. parliament must vote on whether the country can start the process of leaving the European Union. This deals a blow to Prime Minister Theresa May, who had argued that the government on its own could trigger "Article 50" and start the divorce with the EU, despite criticism that this was unconstitutional.