"With Guy Verhofstadt we are showing an example of uniting our forces. I believe that it would be very good also in the national context, in this context in Slovenia, to join forces and have a strong liberal centrist presence in the European Parliament," he said.

Three Slovenian parties are members of ALDE - the Liberal Democrats (LDS) and Zares, which have MEPs but are not in the Slovenian parliament, and the coalition Citizens' List (DL). The ruling Positive Slovenia (PS) will join the group shortly.

Commenting on the PS joining ALDE, Rehn said he was "very happy that we have a strong Slovenian component in the ALDE family now, which I think that Positive Slovenia fits very well because I know there's a very strong centrist liberal tradition in Slovenia."

There has been a lot of talk recently that Janez Potočnik, currently European commissioner for the environment, might emerge as the top name on the ballot of the Slovenian liberal parties, but Potočnik has said he has not taken any decisions to that effect yet.

Asked about Potočnik, Rehn said he was "not going to give any advice to my very good friend Janez Potočnik. I will continue to work with him in the Commission and I believe in the future in the European context as well."