You can't really date Sadler pottery by the gold marks on the bottom, which are the decorators' marks.  However, you can look for numbers on the bottom of the tea set to identify the age. The numbers may represent the manufacturer's code, a pattern number, or its registration number. If the number is the registration number, it will have "rd" following it.

Sadler teapots made between 1899 and 1937 have an impressed mark that reads "ENGLAND JSSB". The early Sadler teapots were "Brown Betty" style, tall, and shaped more like a coffee pot. 

James Sadler and Sons Ltd was founded in 1882 in Stoke-on-Trent, Staffordshire in England. They started with red clay fine earthenware teapots with a dark brown glaze. By 1999 they had 750 product lines.