Mr Jose de Venecia was speaker of the House of Representatives and a close ally of Mrs Arroyo until he fell out with her late last year. He was later removed from the speaker's post.

'I will testify in the House Justice Committee and I will answer all questions,' Mr de Venecia told a news conference. 'My allegations are very strong.'

Asked if this would not implicate himself as well, Mr de Venecia said, 'I will answer all questions no matter who gets hurt.'

Mr De Venecia fell out with Mrs Arroyo after his son named the preisdent's husband in a Senate inquiry late last year into corruption allegations in a state deal with Chinese telecoms firm ZTE Corp.

Mrs Arroyo has denied any involvement in the deal.

Mr De Venecia has said he will testify before the Senate on the deal but has made no move to appear there.

The impeachment case filed against Mrs Arroyo earlier this month is the fourth in as many years. She has defeated the other three with an overwhelming majority in Congress.

She is unlikely to be in any danger this time, despite any possible testimony from Mr de Venecia, analysts say.

Alongside her domination of Congress, she is supported by the army and the powerful Catholic church. Also, her term in office lasts until 2010 and she is not eligible to seek re-election.

Analysts have said political heavyweights are unlikely to join any bid to have her removed by impeachment, preferring to conserve their energies for the 2010 election campaign. -- REUTERS