Plaid Cymru has launched its campaign for the Ceredigion by-election following the decision by the local MP, Cynog Dafis, to step down to concentrate on the National Assembly.

Party leaders told a news conference in Westminster that the campaign would become the "Objective One" by-election - in a reference to the continuing debate over European aid.

Voters will go to the polls in the constituency on 3 February.

Plaid officials rejected claims from Labour that they were "running scared" by holding the by-election so quickly after Mr Dafis's resignation.

Register row

It has emerged that the election will take place using an electoral register compiled in October 1998.

A spokesperson for Ceredigion Council - which is charge of the register - admitted that a number of people living in the constituency would not be allowed to vote.

The council confirmed that a new register would not come into force until 15 February - almost two weeks after the by-election.

The spokesperson said it was impossible to estimate how many people would lose out - but the figure was expected to be less than 5,000.

The only party that has finished selecting a candidate for the Ceredigion seat is Plaid Cymru.

The party has chosen 36-year-old Simon Thomas, a rural development manager.

Meanwhile, Mr Dafis was forced to pass through security checks on Wednesday morning, on his return to Westminster.

Restricted access

Just hours after his resignation the former MP was forced to queue up with tourists and the general public outside the Houses of Parliament.

He no longer enjoys unrestricted access to Westminster.

Mr Dafis, 61, has been an MP since he won the former Liberal seat of Ceredigion and Pembroke North.

His majority over Labour in the 1997 General Election was just under 7,000.

Two other "dual mandate" Plaid MPs - Dafydd Wigley and Ieuan Wyn Jones - are still considering whether to follow the example set by Mr Dafis.

It is thought unlikely that they will give up their Westminster seats before the next General Election - however, a final decison is expected on Friday.