Rishi Sunak is facing further questions over his political judgment after it emerged he was made aware of a complaint by the former chief whip against his political ally Gavin Williamson before appointing him. The Guardian understands some cabinet ministers and ex-ministers were aware of hostile messages to Wendy Morton. The texts were revealed over the weekend to include angry remonstrations about not being invited to the Queen’s funeral and warnings that “there is a price for everything”. The Cabinet Office minister Oliver Dowden defended expletive-laden texts sent by Williamson as sent “in the heat of the moment” after Morton submitted a bullying complaint against him. Conservative Campaign Headquarters (CCHQ) is to investigate the complaint, instead of the Cabinet Office, and Morton had initially asked for her name to be confidential. It comes with Sunak already under pressure over his reappointment of Suella Braverman as home secretary, after she was sacked by Liz Truss for emailing private Home Office documents to a backbench MP. Braverman is also under fire for the deteriorating conditions in the Manston immigration centre, with reports that she ignored legal advice about overcrowding and holding people at the centre too long. Braverman has insisted she took advice into account. Williamson was also reappointed to the cabinet by Sunak, having previously served under Boris Johnson and Theresa May, though sacked by both. The texts were not sent at one particular moment, but on two separate occasions, on 13 September and 17 October. Sunak is said to have been informed by the former party chair Jake Berry of the concerns about Williamson but nonetheless gave him a cabinet position as a minister without portfolio. Dowden said the prime minister was unaware of the contents of the text until Saturday evening. Both Labour and the Lib Dems have called for Sunak to sack Williamson for his behaviour. Williamson has apologised for the messages but Dowden said it was clear they were unacceptable. Dowden said that Sunak was aware there was a “difficult relationship” with Morton, who was chief whip under Liz Truss. “I don’t think it was any secret that Gavin Williamson and other backbenchers had a difficult relationship with the chief whip,” Dowden told Sky News’s Sophy Ridge on Sunday programme. He said the messages, first printed in the Sunday Times, had been sent at what was a “difficult time” for the Conservative party. “These were sent in the heat of the moment, expressing frustration. It was a difficult time for the party. He now accepts that he shouldn’t have done it and he regrets doing so,” Dowden said. “Thankfully we are in a better place now as a party.” Morton is said to have cited the messages from Williamson in an email to the party on the day before Sunak was elected leader. She is also said to have informed the Cabinet Office and accused Williamson of “bullying and intimidation”. Williamson had texted Morton saying it was “very poor and sends a very clear message” that members of the privy council who were not “favoured” by Truss were being deliberately excluded and said it looked “very shit”. “Also don’t forget I know how this works so don’t puss [sic] me about,” he wrote. “It’s very clear how you are going to treat a number of us which is very stupid and you are showing fuck all interest in pulling things together,” one message said. “Don’t bother asking anything from me.” Another read: “Well let’s see how many more times you fuck us all over. There is a price for everything.” Berry said in a statement to the Sunday Times: “In compliance with protocol, in my capacity as party chairman, I informed both the new prime minister and his incoming chief of staff about the complaint on the same day.” Williamson, on Saturday night, stated: “I, of course, regret getting frustrated about the way colleagues and I felt we were being treated. I am happy to speak with Wendy and I hope to work positively with her in the future as I have in the past.” Dowden said no decision would be made about Williamson’s future until the investigation into his behaviour was completed. He said Sunak had not seen the full messages until last night. “He shouldn’t have said it. He has said that he regrets doing so. He has given or has given some context, which was that this was at the time of heightened frustration. It was, remember, him as a backbencher to the chief whip. However, there is this complaints process ongoing and it was not the case that the prime minister had seen this exchange,” he told the BBC One’s Sunday with Laura Kuenssberg programme. Asked if Sunak had confidence in Williamson, Dowden said: “Of course the prime minister continues to have confidence in Gavin Williamson.” The shadow climate secretary, Ed Miliband, said the decision to promote Williamson called into question Sunak’s judgment. “What it says is that Rishi Sunak was making decisions simply in his own narrow short-term interest as far as the Conservative party leadership was concerned, not the national interest, and there needs to be an urgent independent investigation into exactly what happened,” he said. “We can’t have a cover-up, we can’t have a whitewash here.”