Mike Ashley has stepped up his campaign for an investigation into the collapse of Debenhams, claiming MPs are more interested in their own PR than rooting out corporate wrongdoing.

In a two-page letter to the MP Rachel Reeves, seen by the Guardian, the Sports Direct chief executive wrote: “No one in parliament seems sufficiently interested about the Debenhams failure.” He compared this with the collapse of Thomas Cook.

Reeves is the chair of the business, energy and industrial strategy select committee, which is investigating the failure of Britain’s oldest travel company. In his letter, Ashley contrasted the committee’s critical scrutiny of Thomas Cook with its apparent lack of interest in Debenhams.

The committee strongly criticised Thomas Cook’s management in parliament last week for failing to accept responsibility for any wrongdoing. In the letter, Ashley said he had met Reeves and other members of the committee to air concerns about Debenhams but was disappointed they were not “properly investigating”.

He added: “It is very apparent that a head of steam is developing in the media and in the electorate that they will not tolerate these sorts of situations any longer, where businesses and advisers profit from playing the system at the expense of others.”

He claimed politicians and regulators were only interested in their own PR and in cases such as Thomas Cook and Carillion, while ignoring “cases which are just as bad if not worse”, such as Debenhams, Goals Soccer Centres and House of Fraser – all Sports Direct investments that have fared badly.

Ashley’s Sports Direct group spent about £150m on a near-30% stake in Debenhams, but was wiped out when the department store collapsed into administration in April. In the letter, the Sports Direct chief executive highlighted the “material and life changing” loss of money among small shareholders when Debenhams collapsed.

He urged Reeves to confirm that, given its “obvious engagement” in Thomas Cook, the committee would “take immediate steps in relation to the Debenhams situation, as we had previously invited and encouraged you to do”.The Guardian has approached Reeves for comment.

Following publication, a spokesperson for Debenhams said: “It is wrong and irresponsible to compare Debenhams with cases such as Thomas Cook or Carillion. Despite the repeated efforts of Sports Direct to destabilise the business, Debenhams continues to trade and employ 25,000 people under supportive new owners who are investing substantial sums to ensure a sustainable future.”