Yonyuth Wichaidit has resigned as leader of the Pheu Thai Party and from his seat as a party list MP, party leader Prompong Nopparit said on Thursday.

The resignation took effect from today.

Mr Prompong said this was Mr Yongyuth's second important decision to allow the party to be restructured and make way for members of a new generation to take over his former positions while he awaits official rulings on his eligibility to serve on the cabinet, to hold the party leadership, and to be an MP.

Mr Yongyuth had earlier resigned from the dual posts of deputy prime minister and interior minister after the National Anti-Corruption Commission (NACC) found he committed malfeasance in handling the Alpine land case in 2002 when he was deputy interior permanent secretary, and the Interior Ministry's civil service committee subsequently dismissed him, retroactive to 2002.

The Pheu Thai spokesman said Mr Yongyuth had shown political spirit and set a political standard in not clinging to any position.

His actions in resigning were not to evade being scrutinised, Mr Prompong said.

On Wednesday, the Democrat Party filed a requested, backed by 62 MPs, for House Speaker Somsak Kiatsuranont to ask the Constitution Court to rule whether Mr Yongyuth is still qualified to be Pheu Thai leader and an MP.