I contributed to a collected article published by LSE on MEPs’ views about the UK referendum.
The role of the European Parliament in the UK’s renegotiation saga could be crucial or minor — depending on how the talks go — and in the ultimate case of an eventual Brexit, decisive as regards the terms and conditions for subsequent arrangements.
For the “reforms” Cameron is seeking, much depends on the instruments used to secure them. If changes to existing EU legislation are required, then these must get through the (possibly reluctant) Parliament. If a treaty protocol is the instrument of choice, then there is no formal European Parliament veto (though in certain circumstances, it could insist on a Convention to examine the changes and probably propose others), but the approval of 28 national parliaments will ultimately be needed. If the reforms consist of jointly agreed interpretations of the treaty (whether or not these are lodged with the UN) or changes to Council’s Rules of Procedure, or undertakings entered into by the Commission or by Member States, then there is no formal role for the Parliament, but it will certainly be a major forum of political debate on them, contributing to the shaping of opinion in political parties across Europe.
Finally, if there is a Brexit, the European Parliament has a veto over any terms negotiated for future arrangements.