In the good old days, Formula Libre was for anything on 4 wheels, but changed later for open wheel or closed wheel classes. At Brands in '75, Gerry Marshall and DTV entered Baby Bertha for a laugh, ending up winning and beating Philip Guerola's F. Atlantic March.
Not sure who took the pic below, taken from Gerry's book 'Only Here for the Beer' with no mention but credit to them.
Formula Libre should be encouraged today in my view, too many small grids, too many exciting cars hidden away with nowhere to race. Also too many club level championships. A series of libre races for fun with no championship to worry about, which club level racing is all about. The Eight Clubs races at the Walter Hayes show how much fun and how good 'libre' racing can be.