Jim Broadbent who played Roy Slater was the original choice to play Del-Boy (but wouldn't commit to anything beyond two series) The role went to David Jason with Broadbent cast as the recurring character, Slater.
In his autobiography, David Jason described Roy Slater as "a particularly lizard-like copper". Jason was amazed that Jim Broadbent went from humble beginnings here to amazing places like The Borrowers (1997) and Hollywood and wondered why he didn't take Jason with him.
Del talks about someone " ...going down the Kermit.. ". This is elaborate cockney rhyming slang; Kermit= Kermit the Frog = Frog and Toad= Road (meaning in this case, prison).