Described here:
www.gersociety.org.uk
Massey Bromley was the Chief Mechanical Engineer of the Great Eastern Railway at the time, and it is normal to attribute locomotives to that officer, although the actual design would be done by his drawing office. Some locomotives might be built by the railway's own locomotive workshops, which for the GER were in Stratford, while others, including these, would have the drawings issued to mainstream locomotive factories. Dubs were in Glasgow, and Kitson were in Leeds, they built 10 each. The locomotive type, or class, was often known by the number of the first one, although the classification applied to all. These were the 245 class. Dubs built 245-254, and Kitson built 600-609. The floral appearance of the cover (the "splasher") over the large driving wheel shows it is early in the loco life, as later these were replaced by plain steel covers.
This reference states that four were stationed at Yarmouth, and although built in 1879-1882, they were all scrapped between 1890-1893 as now being outmoded, which may help you date the photograph
locomotives of the Great Eastern Railway built at Stratford under Gooch, Sinclair, Johnson, Adams, Bromley, Holden and Hill
steamindex.com
If your grandfather was the driver it was not uncommon in Victorian times to be issued with his own locomotive, which he principally drove and took responsibility for, including arranging for repairs etc. I don't suppose your grandfather is here too?
rchsimagearchive.org.uk