Labour's former deputy chairman Tom Watson has attacked the professionalism of Ed Miliband's press operation, saying some advisers should cut out elementary blunders or resign. He said there was deep concern in the shadow cabinet about the way Miliband's office operated. The party needed to sharpen up if it was going to win the next election, he said.

Watson, MP for West Bromwich East, was renewing his assault on Miliband for posing with a copy of the Sun on Thursday to back the England football team before the World Cup.

Faced by an outcry by Merseyside Labour MPs and the Liverpool executive mayor, Joe Anderson, Miliband subsequently issued a partial apology to those who were offended, which annoyed the Sun.

Speaking on BBC Radio 5 Live, Watson, a long-term campaigner against phone hacking at the Murdoch newspapers, said: "I think it was a serious mistake and it's done a lot of damage to our base." Watson said Miliband was very badly advised, though appearing in the photograph was his ultimate responsibility.

Miliband should have been alert to the dangers, Watson added. "But look, the people around Ed, they're not civil servants. They're very powerful political people; they carry a lot of power in the Labour party. A lot of Labour members raise funds to pay their very good salaries and to make elementary blunders like this in the week that the Hillsborough inquests were taking place … I think it's a problem.

"I'm sure they'll be a lot of shadow cabinet members who are holding their counsel on this, but they are worried about the way Ed's office operates, and particularly the press operation."

Asked what the advisers should do, Watson said: "They've either got to lift their game or move on and get people who can do the job, in my view."

It emerged at the weekend that the photograph was not cleared with Miliband's political office.

Watson said the fact that all three party leaders, "had to go through the indignity of a photograph to help the Sun's newspaper marketing campaign" raised questions about whether politicians had truly learned the lessons of the Leveson inquiry.

"Rupert Murdoch is still all-powerful, sitting over there on the east coast of America, glowering, furious with politicians of all political parties for putting him under a bit of scrutiny."

He said the party had the right message on the cost-of-living crisis, but he added: "We've got some of the very best people at the top of the party, but these unforced errors cumulatively leave us in difficulty and it needs to stop.

"We had a leader of the Labour party who was publicly embarrassed on Thursday because whoever was in charge of press let him go through a process where we had councillors in Merseyside resigning. It was a schoolboy error from someone who doesn't understand the Labour party. You don't win elections if you can't build that alliance."

Watson said he did not know which aide was responsible for the decision, and added that it would be unfair to name them.

The former deputy Labour leader John Prescott said he would not have posed for the photograph.