The first year the Lenton was available with derailer gears was 1957... this year saw a lot of changes in that the bikes also went to 27 inch wheels and could have been purchased with a Benelux 4 speed and in 1958 the Lenton Grand Prix was equipped with a double chain wheel and rod shifter to make the bike an 8 speed.
The three speed models remained very popular as these were a solid and established technology and actually are a much better drive system than those early pull chain derailers.
The Reg Harris editions were also a little different than the base Sports model.
Raleigh also offered the Cyclo Benelux 3 speed conversion for the SA hub to make it a 9 speed model.
You won't see many 1950's Raleigh's or pre 1960's bikes around here unless you are hanging out in my shop... if people have them they aren't riding them like I do.
My Lenton was purchased as a fixed gear model and with the transfiguration of the Sports I now have a decent 3 speed wheel for it if I wanted to rock another gear... the 3 speed model was also a few dollars more than the fixed gear.