U.K. lawyers have expressed their concern following the resignation of Attorney General Geoffrey Cox, who left his post as part of Prime Minister Boris Johnson's cabinet reshuffle on Thursday.

In a tweet sharing his resignation letter, Cox announced he is "leaving the government at the PM's request".

Richard Eccles, competition partner at Bird & Bird, said the resignation was concerning, particularly given the impact of Johnson's proposed constitutional reform in relation to the courts:

"The resignation of Cox is worrying in the light of the government's – or at least the PM's office's – proposals to redefine the scope of judicial review and possibly enable lower courts to depart from European Court judgments on retained EU law, which may suggest an undermining of the rule of law."

One partner at a U.S. firm in London expressed surprise at the decision, suggesting that it comes across as "sacking somebody who is doing their job".

"You never really know what's going on but he was kept on from Theresa May's time, a Brexiteer and appeared to be fairly candid and forthright. Perhaps he was telling Johnson things he did not want to hear, or maybe he didn't have the commitment to the reforms that Johnson is focusing on."

The partner also pointed to the "dark mutterings around Johnson's constitutional reform", which would narrow the Supreme Court's and other courts' ability to hold the government to account.

The partner added that there will be extra focus on who is appointed to replace Cox in the role, saying: "It is a question of whether somebody will be sent to do a hatchet job on the judiciary."

One regulatory and trade partner at a U.K. firm said the departure of Cox was no surprise. "He was going to be fired anyway", they said, "partly because he stood up for the courts and the rule of law."

"Let's see who will be next: will it be someone who continues to uphold that or someone who gives the government the answers it wants to hear?"