Burges Salmon has been forced to postpone the appointment of its new managing partner Paul Haggett because he is snowed under with case work.
Instead, the firm has had to make its senior partner David Marsh acting managing partner.
Haggett was elected managing partner in February but has yet to take up the post.
His predecessor Guy Stobart stepped down to concentrate on his role in the firm's finance team.
This has left Marsh to fill in at the 40-partner Bristol-based firm.
Marsh says: “Paul is too busy to take up the position now. He has big cases that are taking up more time than we expected.
“I will be standing in for him for six to 12 months. It depends on how long his cases go on for.
“Of course, we did not know this when we elected him.”
Marsh has been managing partner before. He was elected to the position for two terms from 1989 until 1995.
Unlike Haggett, Marsh has not been voted into the post of managing partner, but a spokesman for the firm says he was chosen with the support of the partnership.
He adds: “There are other people helping David in his two roles, such as business development partner Bob Smyth.”