A government-appointed commission is taking evidence from interested parties this week ahead of the publication of a report on whether the Act should be changed.
But Information Commissioner Christopher Graham, who oversees the FoI system and handles appeals from people who have had requests refused, has backed the status quo.
He said the existing public interest exemptions were adequate when it came to protecting discussions between ministers and their advisors.
Mr Graham said: “It would be a great mistake to go for an absolute exemption in areas where it is currently qualified by a public interest test.”
He added that there was “no case for rewriting the legislation” to exclude advice given to ministers by civil servants.
Mr Graham said that the rise in the number of refusals for requests upheld by his office from 69pc in 2014 to 83pc in 2015 was evidence that the current system is working.
And he suggested the commission – widely expected to recommend a watering-down of the Act – that it should consider extending it to cover private contractors delivering public services.
The commission is chaired by former Treasury mandarin Lord Burns and includes several FoI sceptics including former Tory leader Michael Howard and former Home Secretary Jack Straw.
Liberal Democrat peer Lord McNally, who also appeared at yesterday’s evidence session, has described the commission as a “rigged jury”.