Poland's Nobel Peace Prize winner and former president Lech Walesa on Thursday urged Poles to ratify the draft constitution for the European Union in order to "improve it from within."

"The constitution, as it stands today, is not good, but we can only improve it from within," Walesa said on public radio.

"In other words, we have to ratify the constitution and then work to ensure that elements of it which are unacceptable are improved upon. Rejecting the constitution in a referendum would be a big mistake," he said.

Poland's ruling leftwing coalition, which is in favour of the EU constitution, wants a referendum to be held on it at the same time as presidential elections, due in October.

But the centre-right opposition -- against the constitution -- wants the plebiscite to be held next year, to allow Poland to see what results arise from referenda in other EU member states, including euro-sceptic countries such as Britain.

According to opinion polls, nearly 60 percent of Poland's electorate are in favour of ratifying the draft EU constitution.