In the early 1970s Lambert tried to design their own derailleur and had a notable lack of success. So Lambert took an obvious step - and bought-in a Taiwanese copy of the best selling, lowish-end, derailleur of the time, the Shimano Eagle SS.
I believe that this Lambert model was manufactured by SunRace. It is a moderately decent quality object, just slightly less accurately made, just slightly heavier and with just slightly flakier chrome than the Shimano.
Lambert had a reputation for pushing the envelope of affordable bicycle design. On the one hand, this derailleur is the antithesis of that reputation - you could not get more mundane or mainstream that a Shimano Eagle SS. On the other hand this is among the very first Taiwanese components that I can remember seeing on a UK branded bicycle. Today, of course, many British branded bicycles are not only manufactured in Taiwan, they are also liberally festooned with Taiwanese components.
Browse associated documents.