* Blow to prosecutors in scandal that brought down PM Necas
* Prosecutors may try to reformulate charges
* Necas's aide still charged with bribery, illegal spying
By Jan Lopatka
PRAGUE, July 26 (Reuters) - The senior Czech prosecutor withdrew bribery charges against three former members of parliament on Friday on the grounds they had immunity, weakening a wider case against corruption that led to the fall of Prime Minister Petr Necas.
The MPs were accused of accepting posts at state firms.
Supreme prosecutor Pavel Zeman cancelled charges after a court ruled last week that they were covered by parliamentary immunity. In return, they agreed to leave parliament.
"The Supreme Court decision is surprising to me," Zeman told a news conference. "But it is fundamental in a country with rule of law that we not only respect court decisions but apply them as well."
The scandal threw the central European country into a political crisis which could still last for months as parties squabble with President Milos Zeman - who is unrelated to the prosecutor - over the appointment of a new government.
Necas stpped down in June. He was not charged in the case but his senior aide Jana Nagyova, with whom he has a relationship, was accused of arranging the bribery and also illegally asking military intelligence to spy on Necas's wife.
Prosecutors said their investigation of Nagyova and the deputies was part of a wider investigation into corruption, which many Czechs see as widespread in national politics.
Nagyova and four other people still face prosecution, some for corruption and others for allegedly abusing the role of the secret service, Zeman said.
The investigation raised hopes among Czechs that police and state attorneys had found the muscle to bring dirty politicians to justice. But no-one has been charged in the wider graft investigation so far and the partial collapse of the bribery charges weakens the case further.
Necas has insisted that political negotiations cannot be considered a crime and also denied there was any outright agreement the deputies would swap their mandates for posts at state firms. A lawyer for Nagyova said she acted in good faith.
Zeman said prosecutors may try to reformulate their case so the deputies can be charged again.
President Zeman's cabinet faces a vote of confidence on Aug. 8 which could prolong the political instability. Attempts to form a new cabinet may follow unless the parties agree to dissolve parliament and hold an early election.
(Reporting by Jan Lopatka; Editing by Angus MacSwan)