Just got an email from Mark Thomas:
"Lawyers acting on behalf of Mark Thomas served Speaker Martin with legal papers demanding am independent audit and investigation into the scandal of MP's expenses. The audit should examine all claims going back to 1997, not just the last four years, any mispayments or misclaimed expenses should be repaid rather than rely on voluntary repayment when MP's feels adequately embarrassed and if there is evidence of fraudulent claims then the police should be called in to investigate. MP's should be subject to the same standards and laws as the rest of us.
If Speaker Martin does not launch an independent investigation then Mark and the lawyers will seek a judicial review of his actions. "
You can find more details of exactly what he's planning from his website.