This is probably one of my favourite small size steam engines i've seen and it does bear a striking similarity to a Stuart 10H, the main difference is the crosshead and base are all a single casting unlike the Stuart.
'The Westminster Engine' was made by Edward Bennis & Co of Bolton and it was most likely offered as motive power for the companies range of mechanical stokers as well as a general purpose workshop engine.
Here is a nice print of one:
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And a photo i took of a working example at Claymills Pumping Station:
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