Diffcult to see properly wthout a higher resolution scan but those look lke punts in the background.
Could be near Oxford
Salters Steamers still operate boats that look similar to that in the picture
possibly a Salter's built boat for Joseph Mears? (Going on the M on the 2 visible lifebelts)
Mears ran trips from London out towards Henley etc. The Dept of Explosives had a building at Storey's Gate, Westminster, SW1 not far from Westminster Pier which was one of the stops for Mears boats.
Might be worth sending the image to the website owners at the following link to see if they can confirm the boat as either a Mears or a Salters vessel (my guess is the Richmond Belle from Mears). http://www.simplonpc...esLaunches.html
They have a collection of postcards and may know the photographers name. George Bushell appears to have been an active photographer in Market Place from 1919 onwards but I'm finding nothing re a Mreches or variation of this name
Was 24th May Empire Day in 1919?
Ancestry has a number of medal index cards for officers with Ministry of Munitions (and variant spellings) entries e.g.
Capt Thomas North Whitehead, ASC
Lt Richard Barclay Williams, RE
Lt A H Campbell, RE
T/Capt Clifford Haydon, ASC
plus a number who were RFA, RGA, RH & RFA, RA
Finding images of the officers (and civilians) to match with the photo is proving difficult.