Richmond upon Thames College, formed out of an FE college and two sixth-form colleges in 1978, is under threat from local Conservatives who want to allow all the borough's eight secondary schools to bring back sixth forms.
One church school in Sheen, Christ's, has already tried to set up one, and the Tories hope that others will follow suit.
The man advising the Conservative candidates on secondary and post-16 education policy is Donald Naismith, the borough's former director of education, who created the college when the Tories were last in power 20 years ago. He said that bringing back sixth forms would create diversity for pupils and parents.
"When the college was first created it was intended to serve the whole borough for 16-19 education, but it has rapidly outgrown that stage and expanded enormously. But some students prefer a smaller, more manageable institution," he said.
Mr Naismith admitted that the college, which now takes in under half its students from inside the borough, might suffer from the resurgence of sixth forms.
"It will have to look at the courses it is offering," he said. "It is not our job to prop up institutions. I believe education systems and standards thrive through competition."
Geoffrey Samuel, the Tory education spokesman, a retired headteacher from Hounslow, said: "We will not force schools to do this, but we are confident that many will take up this option."
David Cornwell, outgoing Liberal-Democrat chairman of Richmond's education committee, said he recognised the argument for in-school sixth forms but had not put forward such a policy. "It would be massively expensive. Have the Tories asked themselves where they will get the money from?" he asked.
Eric Kirby, principal of the tertiary college, said he was confident that ministers would turn down any proposal for new sixth forms because the Christ's school initiative had already failed to attract sufficient students. "Not only would they be uneconomic, they would reduce the choice of curriculum for students."
He was "amazed" that Mr Naismith was lending his name to the Tory campaign. "He was not only one of the founders of this college, he was a pioneer of tertiary education.
"His views, like those of the Richmond Tories, seem to have undergone a remarkable sea change just when tertiary education is about to come of age."