It is not every day that one of the City's leading M&A partners steps away from private practice to make the move in-house. John Davidson, a corporate partner at Lovells for more than 20 years, rocked the boat last May when he announced that he was moving in-house to become general counsel at longstanding client SABMiller.

"It is not that it wasn't a difficult decision to make," says Davidson, who had spent his entire career with Lovells. "I would not have gone to any other firm, but SABMiller has a reputation as an exciting place to work and I thought this was a good time to make the move."

Hired to replace company secretary and general counsel Andrew Tonkinson, who retired last August, Davidson is one of the most high-profile senior UK lawyers to have left private practice for the in-house world to date. In contrast, Tonkinson, while a lawyer by training, did not practise law.

Davidson's relationship with the brewing giant began in 1998 when Lovells was named as SABMiller's UK legal adviser on the group's restructuring and relisting of the holding company in the UK. After almost a decade of advising the company through a series of shake-ups, including the 2002 merger with US brewer Miller and 2005′s merger with the second-largest brewer in South America, Grupo Empresarial Bavaria, Davidson's bonds with SABMiller are deeply forged.

"I was involved in the company from a very early stage, but now I have a hand in the strategy side of the business," says Davidson, who is the first practising lawyer to sit on the executive committee. "We have a very US-style board, with only two executives and a pretty straightforward hierarchy."

SABMiller's in-house legal function is run on similarly lean lines. A surprisingly small team for a company with a turnover of more than $15bn (£7.5bn), six lawyers sit under Davidson's command in London, with three focusing on M&A work and three dedicated to commercial matters.

The corporate-focused team has been instrumental in a number of big-ticket deals for the company and last year won recognition when it beat competition from shortlisted teams from Nokia, Goldman Sachs and Permira among others to be named In-house Deal Team of the Year at the Legal Week Awards.

Worldwide, the company's legal function comprises around 70 lawyers across the various arms of the business including local general counsel in Colombia and the US.

"The team is about quality, not quantity," says Davidson. "People here are very receptive to what we do and the legal team is very much seen as a valuable part of the business. The company's structure is such that many of the businesses have their own legal teams."

Davidson, however, says he has no plans to set up a panel or to overhaul the company's adviser roster. Lovells, with Davidson's former colleague Andrew Pearson as the new client relationship partner, remains the company's main corporate adviser. The company also instructs Werksmans in South Africa, Richards Butler in Hong Kong and Stevens & Bolton for employment matters in the UK.

Davidson's influence on the in-house team at SABMiller saw him advise on the secondment from Lovells of the company's first in-house lawyer in 2002. Davidson is a strong advocate of the rotating six-month secondment scheme, which the company runs with Lovells throughout the year.

"There are people who can come straight in and are able to add value and be creative," he says, adding that being a secondee gives a private practice lawyer an invaluable opportunity to see things from a client's perspective.

In-house should not be seen as an easy option, however. Davidson warns that any move should be carefully considered: "They have to recognise the challenge. Being in-house can be a much more lonely position than private practice."

Isolation is not worrying Davidson so far. He was invited to join the FTSE 100 general counsel group, the GC100, shortly after he took up his new role. The group, which recently elected National Grid general counsel Helen Mahy as its new chair, is currently campaigning on a number of issues surrounding the Companies Bill and, Davidson says, is coming into its own as a representative body.

"The GC100 has gelled into a really effective team and support network," he says, adding that he fully supported the GC100′s move last month to extend membership to company secretaries.

When asked what is currently on SABMiller's agenda, Davidson is coy, but the company's move to appoint such an experienced M&A adviser suggests that it does not plan to dampen its acquisitive spirit any time soon.

Last year, while still at Lovells, Davidson navigated SABMiller through a hat-trick of deals with an aggregate value of more than £2bn. However, while the company is listed in the UK, the lion's share of its business is located elsewhere around the globe, with operations in 60 countries and big-name brands such as Corona, Peroni, Miller Lite and Nastro Azzurro under its belt.

While international expansion plans may be on the boil for the ambitious group, Davidson is quick to point out that SABMiller has not forgotten its roots and still looks to expand further in Africa, where it currently has operations in 29 countries and is the continent's largest brewer. "The South African business is our heritage," he says. "It is the jewel in our crown."