Poland should push ahead with a referendum on the European Union's troubled constitution in October despite the bloc's decision to extend the deadline for ratification, a senior official told Reuters on Friday. Presidential aide Dariusz Szymczycha criticised those in the centre-right opposition who want to scrap the referendum after the Dutch and French "No" votes, saying such a move would confine Poland to the "sidelines of Europe". "I am strongly in favour of the referendum in October. If we don't vote this year, then new groups which take power will not give us another chance," said Szymczycha, a senior aide of leftist President Aleksander Kwasniewski. Resurgent centre-right parties are expected to defeat the ruling Social Democrats in September parliamentary polls and they have made clear they want to either postpone or abandon plans for the EU vote. Before the start of an ongoing meeting of EU leaders in Brussels, Kwasniewski said Poland -- which joined the EU last year -- may delay its referendum if the June 16-17 summit proved inconclusive. --More 2344 Local Time 2044 GMT