The European Council Decision, taken in agreement with the UK on 11 April, includes a duty of sincere cooperation in relation to the extension of Article 50. This includes reference to “the commitment by the United Kingdom to act in a constructive and responsible manner throughout the extension”. The full Decision can be found here: https://www.consilium.europa.eu/en/press/press-releases/2019/04/10/20190410-european-council-decision-on-extension/.
If the Withdrawal Agreement has not been ratified by 22 May, we have a legal obligation to hold European Parliament elections as a Member State, as set out under EU treaties, and we will uphold these obligations. We have therefore already started making the necessary domestic preparations in order to prepare for this potential outcome. However, as the Prime Minister has said, we will make every effort to ensure the Withdrawal Agreement is ratified by 22 May so that we do not need to hold these elections.