Van Brempt told EUobserver on Tuesday (18 October) that she had a lengthy phone conversation with Liikanen, who was EU commissioner for industry from 1999 to 2004.

“It is not that he did not want to come, but he said he really did not remember anything relevant from that period,” said the centre-left MEP.

“I want to keep the quality of the hearings high.”

Van Brempt referred to the testimony of former commissioner Stavros Dimas, who was in charge of environmental affairs from 2004 to 2010.

“Dimas was very charming, but he said 'I don't remember' quite often,” said Van Brempt, noting that the mandates of Liikanen and Wallstroem dated back even further than that of Dimas.

Wallstroem, commissioner for environment from 1999 to 2004, is currently Sweden's foreign minister and deputy prime minister, and Liikanen is governor of the Bank of Finland.

The EU parliament's inquiry committee will instead send them written questions, and in a summary of their coordinators meeting said they “took note” that the pair had “declined the invitation to a hearing”.

Liikanen's spokesman confirmed to EUobserver that the former commissioner will answer written questions from the committee.

MEPs have not given strong reaction to the no-show, as they did when former industry commissioner Guenter Verheugen initially did not want to show up.

The committee asked parliament's president Martin Schulz to intervene to force Verheugen to appear.

Van Brempt did not play the Schulz card this time, saying: “You have to have a good reason for that.”

Van Brempt also said discussions with French environment minister Segolene Royal were ongoing. Royal has promised to appear, but the two sides have not been able to find a suitable date.

The committee is trying to find out if EU and national authorities could have done more to prevent or find out carmakers' emissions on the road is much higher in the real world than in the laboratory.