I've since managed to acquire a couple of examples of the OG bottles and the colour variation of the bottles and caps is quite interesting. The left hand one is 1962 dated and maker marked 'Cascelloid' and 'Cascaflex' on the base. Interestingly, Cascelloid was the company that gave the world the Action Man doll:   http://www.museumofchildhood.org.uk/collections/british-toy-making-project/toy-manufacturers/palitoy   The other is 1964 dated and maker marked 'F&G'. (currently unidentified)