In 1866 the optical instrument makers of Charles Baker ,244, High Holburn, London ordered from Thomas Cooke & Sons a Barlow lens of power either 300 or 350. Also purchased was an astronomical eyepiece, unfortunately I don’t know the power.
The firm of Charles Barker had been formed in 1765 at the above address and they sold optical and surgical equipment. In the mid 1850s they were also selling not only telescopes but also microscopes and accessories.
The firm was acquired by Cooke Troughton and Simms in 1959.