Five was unavailable for comment this morning, but TV production trade magazine Broadcast, quoting "sources close to the broadcaster", and The Daily Mail have both suggested this morning that such a move is being considered.
The company's interest in pay-TV has been flagged before and discussed by chief executive and chairman Dawn Airey, but it had appeared that its rethink only encompassed its digital channels Fiver and Five US.
Moving its main channel away from free-to-air would substantially reduce commercial impacts and mean Five would have to renegotiate deals for acquired shows.
Broadcast also claims that the company is looking at introducing paid-for video on demand services on Project Canvas, the internet-linked Freeview platform it is developing with the BBC, ITV and BT, or on the SeeSaw platform being developed by Arqiva and based on Project Kangaroo technology.
The chief executive of Five's parent company RTL, Gerhard Zeiler, told the Edinburgh Television Festival in August that all free-to-air broadcasters mustlook at what part of their offer could work in a "pay environment".
The news follows Five's launch yesterday of a £3.99 iPhone app to watch live streaming of its Uefa Europa League football coverage.