Conservative Party leader Colin Craig says he's ready to contest Epsom if it comes to a by-election in the seat held by ACT leader John Banks.

Mr Banks is under scrutiny over whether he declared donations to his 2010 Auckland mayoral campaign as anonymous, but was actually aware of their source.

National Party president Peter Goodfellow is not ruling out a possible deal with the Conservative Party.

ACT got fewer party votes than the Conservatives at last year's election.

Mr Craig says National and the Conservatives have common ground where they could work together.