Are treaty changes needed to meet UK demands, will the four freedoms be safeguarded and could current talks release an avalanche of reform requests from other countries? These questions were put by members of Parliament's constitutional affairs committee to Jonathan Faull, head of the Commission's task force for strategic issues related to the UK referendum, in a debate on Thursday morning.
Other issues brought up by MEPs included involvement by national parliaments in EU decision-making, ways to avoid abuse of welfare systems and how a possible deal would affect the work of the European Parliament.
Mr Faull described the ongoing negotiations as very difficult but marked by a strong desire to reach an agreement that would be good for all parties. The kind of reforms needed at EU level would depend on how EU heads of state or government agreed to respond to Cameron's demands, he added.
EU leaders plan to agree on a deal in response to prime minister Cameron's requests for reforms at the next meeting of the European Council (on 18 and 19 February).