Southwark's further education college formally became part of Lewisham College on Wednesday.
The combined college will be known initially as 'Lewisham College incorporating Southwark College' and is led by Lewisham's incumbent principal Maxine Room CBE.
Although both colleges are describing the move as a 'merger', the Southwark College corporation has been dissolved and its assets and liabilities transferred to the corporation of Lewisham College.
With more than 20,000 students Lewisham College becomes one of the largest further education bodies in London.
"At last a stronger and more secure further education college for Southwark has come into being," said Simon Hughes MP on Wednesday.
"It is a tribute to the two governing bodies, the Skills Funding Agency, the Department of Business, Innovation and Skills, and not least to the two principals of the two partner colleges, Ruth Gilbert and Maxine Room, that today's merger has taken place.
"The next job is to build up the profile and range of courses provided by the new college to maximise the chance for local people of all ages to gain the skills and qualifications they need for the job market of today and tomorrow."
At a meeting with the principal this week the Bermondsey and Old Southwark MP also discussed a new name for the enlarged college.
He urged Ms Room to recommend to the governors that the college should have a name that reflects Lewisham and Southwark component parts in an equal way.
The chairs of the two colleges, Christine Rose from Lewisham and John Landeryou from Southwark, will be on the board of the combined college.
For the time being both colleges have retained their own websites and are continuing to recruit for the 2012/13 academic year under their own identities.