Bart Bassett has become the ninth state Liberal MP to join the crossbench after a corruption inquiry into illegal donations was formally widened to examine allegations that Nathan Tinkler's property development company improperly sought to influence him over a housing development.

Mr Bassett, a former mayor and the member for the seat of Londonderry in western Sydney, announced on Wednesday afternoon that he would "stand aside" from the parliamentary Liberal Party during the inquiry.

Londonderry MP Bart Bassett: ''I reject this allegation.'' Credit:Kylie Pitt

"I reject this allegation and I look forward to my opportunity to clear my name," Mr Bassett said.

Mr Bassett joins six of his colleagues on the crossbench, including former ministers Mike Gallacher and Chris Hartcher. Another two MPs, Tim Owen and Andrew Cornwell, have since resigned.