In the assembly elections in May, the party almost trebled its share of the vote and emerged as the main opposition party.

The scale of that advance is evident in the Conwy constituency in north Wales, where the conference is being held on 23 September.

In the general election, Plaid was in a poor fourth place with just 6% of the vote. In May, it leapfrogged the other three parties and took a seat which had been a key target for both the Conservatives and the Liberal Democrats.

Plaid president Dafydd Wigley

Across Wales, Plaid took 17 of the 60 Assembly seats, including the Labour south Wales Valley strongholds of Rhondda and Islwyn.

That gave Plaid its longed-for breakthrough outside its Welsh-speaking heartlands.

That success was mirrored at the European elections in June when the party came within 2% of overtaking Labour as Wales's largest party.

Success has brought its problems, though. The party has been accused of having too cosy a relationship with Labour in the Assembly, and this week the party president Dafydd Wigley admitted that they had given Labour "an easy ride" in Cardiff Bay.

Gareth Jones took Conwy in a shock Plaid gain

The party's leaders plan to use the conference to distance themselves from Labour and to warn that should the administration in Cardiff fail to deliver in a number of key areas, the party will not hesitate to bring the government down.

The party is likely to highlight the securing of matching funds from the treasury for European grants as one issue that could lead to the fall of Alun Michael's government.

The new radicalism is partly an attempt to silence critics within the party but on one issue the division between the pragmatists and radical wings is certain to be highlighted.

The radicals are fundamentally opposed to the party accepting any offer of additional seats in the reformed House of Lords - a move which the party leadership regard as an important means of strengthening the Plaid voice at Westminster.