A fair number of people switch between the two arms of the profession, but it is rare for someone of Mr Brodie's seniority to make the move. He acknowledges that it will, initially at least, necessitate a change in status. 'As a senior member of a law firm, you are at the top of the team. At the Bar I will certainly have to begin lower down, in some instances right at the bottom,' he says.
Mr Brodie has been granted exemption from exams - 'thank heavens' - but will, he says, undertake a 'voluntary bringing up to speed'.
'I will read a lot of law and I will have to develop a number of skills that I've either forgotten or have only partially developed. But there's a stock of many years' experience I will be able to bring, that young men and women going to the Bar won't have had.'
When he joins the Bar next year he will undertake a six-month pupillage before being allowed to practise on his own account. 'I may be able to do a certain amount after three months if I get good marks from my pupil master, Anthony Seys Llewellyn,' he says.
This will not be the first time Mr Brodie has retrained. When he came to England from his native South Africa, he had to retake articles. At first, he worked for a firm specialising in insurance litigation, and transferred to Frere Cholmeley in 1968. Since then he has worked almost exclusively in civil litigation and arbitration. For the past six years, he has also been heavily involved in the management of the firm.
What makes his move unusual, Mr Brodie agrees, is that it is happening at 55, not 30. 'But in one way, it's far easier for someone at my stage of life to do this because I have no children at school or university. I am not faced as younger people are with a crunching mortgage. I have a degree of independence that comes from spending a lot of years in a successful practice,' he says.
He adds that there is nowadays an increasing tendency for people to embark on second and even third careers. 'I have always thought it likely that I would make a career change at some point in my fifties,' he says. 'Temperamentally, I am not someone who wants to retire. I had got to the stage where I was coming to the end of my term as chairman of the firm. I decided not to put myself forward to continue in the job and to do something different.'
He considered a number of possibilities, including government work, before plumping for the Bar. One of its attractions for him was the independence of its practitioners. For one thing, he says, this means that he will be competing only with himself, and not with 25-year-olds. But it is an ironic choice in some ways, he says, because of his long-held view that the two branches of the profession should come closer together.
Mr Brodie's decision has met two overwhelming reactions. 'My non-lawyer friends think it's wonderful. The lawyers are sharply divided,' he says. 'Some are gloomy, they think I'll be disappointed and some are disturbed by anyone doing something different. The others are very enthusiastic.'
His colleagues at Frere Cholmeley did try to dissuade him from leaving, he says. 'At first they said think again, do you really want to do this? Have a holiday, get that nonsense out of your head, then we'll find something else for you to do, pick what you want. Some people also expressed regret. After that, they were supportive.'
His clients have been enthusiastic. 'The firm has a collegiate culture and the work we do for clients is distributed among the team. The aim is to develop a relationship with clients where they don't feel that the presence of any one partner is the be-all and end-all. That would be dangerous. So the fact that I'm going will not mean that clients are not going to continue to use the firm and be happy with the service.'
Mr Brodie looks back on his working life with Frere Cholmeley as a happy and rewarding time. 'Although I will have made numerous mistakes managing the firm, I am very happy with the way it has developed, particularly in Europe.'
Another development has been the firm's recent move to an attractive new building in John Carpenter Street. 'It is ironic that I am leaving immediately after the shift, as I have promoted the move for years,' Mr Brodie says.
'But now I feel I need to do something different, something that makes the sap rise. Part of me says if you are prepared to roll the dice in these difficult financial times, why not do nothing, travel the world. But I suspect that paradise stretching into infinity loses its savour.
'I'm sure I will have a great deal to get used to and I will miss many people. But I'm lucky to embark on a new career at this time in my life. I may fall on my face but perhaps that's a risk you have to take.'