Today the Prime Minister of the United Kingdom, Theresa May, formally asked the European Union for an extension to Article 50. The deadline requested by May is June 30. This is designed to give the UK’s government three months to smooth over the rougher edges of the deal they negotiated with the European Union last year and try to get it past a parliamentary vote. So far the deal has been formally rejected twice, with a very pronounced bias against.
However, it seems that the European Commission did not take well to the request. The June 30 deadline is inconvenient, as there are European elections in May. This is why EU officials would prefer if the UK chooses either a deadline earlier than that so that Brexit talks do not distract from the elections, or until the end of 2019, in which case the United Kingdom will also participate in the elections. Moreover, according to the EU, the extension will be final (so as not to set a dangerous precedent and enter a loop of infinite extensions). Now the British government need to decide if they can push their deal successfully in about half the time they requested, or take the longer offer and risk losing in a preliminary general elections in the UK, which is what the opposition Labour Party is pushing for.
As a result of these developments the British pound has weakened.