A special meeting of the Council had already been scheduled for 10 April.
The letter also states that the UK government
will "want to agree a timetable for ratification that allows the UK to withdraw from the EU before 23 May 2019 and therefore avoid elections to the European Parliament but the UK will "continue to make responsible preparations to hold elections should this not prove possible."
The letter indicates that further legislation is required to implement the withdrawal agreement and to ratify the agreement. A Withdrawal Agreement Implementation Bill can therefore be expected.
The Guardian 5 April 2019
The European Union (Withdrawal) Act 2018 section 13 prevents ratification of the withdrawal agreement unless the steps required by the section are taken including affirmative resolution of the House of Commons.
The remaining stages of the European Union (Withdrawal) (No.5) Bill are, at the time of writing, scheduled to take place in the House of Lords on Monday 8 April - previous post on the Bill. The political aim of this Bill is to prevent a "no deal" Brexit.
Under the terms of the European Council Decision of 22 March, the UK leaves the EU on 12 April but it is open to the government to indicate a way forward for consideration by the European Council - previous post 22 March.
Political action is under way in London to see whether such a way forward can be agreed.