Government sources have rowed back on Boris Johnson’s apparent commitment to criminal sanctions for tech company bosses who fail to tackle harmful or illegal content.

However, the Guardian understands that the new culture secretary, Nadine Dorries, who has first-hand experience of online abuse, is minded to take a tougher approach on sanctions than her predecessor Oliver Dowden, though she is still taking advice.

During prime minister’s questions, Johnson appeared to agree with Keir Starmer that the delayed online harms bill would include a commitment to possible criminal sanctions.

The proposals already include deferred powers on new criminal offence and the bill already contains the power to issue fines, but any change to immediately implement criminal sanctions would be a significant hardening of the proposals.

Johnson promised to present the bill to parliament before Christmas in the wake of the killing of Sir David Amess. That prospect was also later played down by Whitehall sources, saying that would give them just five days to re-draft the bill between the pre-legislative scrutiny committee reporting and the bill being presented.

Pressed by Starmer on what measures he would take, Johnson agreed with the idea of a cross-party approach but also peppered his responses with partisan criticisms, prompting some shouts of complaint in the Commons.

Starmer began his questions by noting the tributes to Amess, the veteran Conservative backbencher who was stabbed to death at a constituency surgery on Friday, given by MPs from all parties in the Commons on Monday.

“I want to see if we can use that collaborative spirit to make progress on one of the issues that was raised on Monday – tackling violent extremism,” Starmer said, asking about progress for the online safety bill, first mooted three years ago.

Starmer said: “Will the prime minister build on the desire shown by this house on Monday to get things done, and commit to bringing forward the second reading of the online safety bill by the end of this calendar year? If he does, we’ll support it.”

Johnson replied by initially pledging the bill would complete all its stages before Christmas, before correcting himself – seemingly at the prompting of the home secretary, Priti Patel, who was sitting next to him – to say he would “bring it forward before Christmas in the way that he suggests – and I’m delighted that he is offering his support”.

Starmer then pressed on potential changes to the proposed bill, saying: “Tough sanctions are clearly needed, yet under the government’s current proposals, directors of platforms failing to crack down on extremism would still not face criminal sanctions. Why is that?”

In a later answer, Johnson appeared to agree to this, saying: “And yes, of course we will have criminal sanctions with tough sentences for those who are responsible for allowing this foul content to permeate the internet.”