That’s an interesting and possibly rare piece of equipment, you really must give it a try!
I’ve found a piece of text from 1953 which explains it:
“The Fairlawn spreader is made by the Fairlawn Company, Fairfield Works, Buxton, Derbyshire, to fit any normal wheelbarrow and enables accurate distribution of small repeated doses of artificial fertiliser”.
It could spread weedkiller, lime, sand etc at a rate of 1/2 oz to 1lb per square yard. Simple controls and satisfaction guaranteed. Cost was £9/10/0 carriage paid in 1956.
A company called Fairfield International Spreaders were also based at the Fairfield works in 1954.
Interestingly the Fairfield Works have had many uses including the Buxton Mineral water Co. in the late 1800’s.