Nationals senator John Williams will ask the corporate regulator why it didn’t take action against two DJs directors accused of insider trading.

A decision by the corporate regulator not to reopen an investigation into two David Jones directors accused of insider trading will come under the scrutiny of the Senate.

Fresh questions have been raised about the purchase of David Jones shares by two of the company’s directors in October, the same month the retailer rejected a merger offer from competitor Myer.

The offer was kept from shareholders and the public until media speculation prompted the two companies to release details of the proposal this week.

The purchases by Leigh Clapham and Steven Vamos were made days before a better than expected sales result caused a spike in the share price and, according to this week’s information, days after the Myer proposal was lodged.

The Australian Securities and Investments Commission investigated the share purchases. Although it was aware of the merger proposal it decided not to take action against the two directors.

Nationals senator John Williams, who successfully moved for an inquiry into the regulator last year, said the committee would be looking at ASIC’s decision.

“We’ll be seeking more details on insider trading at DJs and asking them to explain to the committee why they made the decision not to take it any further,” he told the Australian Financial Review on Saturday.

Senator Williams has questioned the competence of the regulator in the past and accused officials of stonewalling during budget estimates hearings.