One of Denton Wilde Sapte's highest billers has left the City firm to join top property client London & Regional Properties (L&R) in a move that will be watched keenly by rival advisers.

Leonard Sebastian left Dentons at the beginning of May and, according to the L&R website, has become the company's chief legal counsel and a member of the its five-strong board. It is understood to be the first time the real estate giant has appointed an in-house counsel.

Sebastian will be retained by Dentons as a part-time consultant.

Sebastian has advised L&R for a number of years and was Denton's sole relationship partner for the client. He first acted for the company – which is headed by Ian and Richard Livingstone – in 2003 on a £318m sale of the leaseholds of 280 pubs by Morgan Grenfell Private Equity.

More recently Sebastian advised L&R on its November disposal of a portfolio of Nordic and Baltic properties to Northern European Properties – also run by the Livingstones.

A spokesman for Dentons said: "Leonard left on amicable terms and we hope to work closely with him on further London & Regional transactions."

L&R is one of the largest private property companies in Europe, with interests exceeding €8.5bn (£5.8bn) in a dozen countries, including the Scandinavia, Germany, Poland, Russia, South Africa and Panama as well as the UK.

Current advisers to the group include City rivals Taylor Wessing and Herbert Smith, whose L&R relationship partner, Chris de Pury, is to leave the firm later this year for Berwin Leighton Paisner.