This is a miniature beam engine mounted on a tripod and heated by a candle in a similar manner to the Wilesco D2. The safety valve looks like a standard Wilesco one, but that doesn't mean Wilesco made the rest of the engine. MiniSteam are retailers so it's unlikely that they made the engine themselves. However, it is sold under their brand name. The engine unit itself looks remarkably similar to the Microcosm M81, so maybe it was made by them.
The engine is mounted directly on the top of the boiler, which is supported by a tripod over a candle for heating. The main part of the engine, including the cylinder, valve chest, crankshaft bearing and the support pillar for the beam, is machined from a single block of brass. It is soldered to the top of the boiler, with no pipework.
The boiler is heated by a double wick T-light sized beeswax candle. The boiler is supported over the candle by a tri-pod arrangement. It is a squat vertical cylindrical pot boiler, 50mm diameter x 37mm high. Apart from the engine itself, the only fitting on the boiler is a safety valve. There is no water level indication, regulator or lubricator.
The cylinder is cast into the main engine part; 4mm bore x 7mm stroke. It is controlled by a piston valve connected to the main crank via a linkage. The piston is connected to one end of the beam using a simple connecting rod, with no parallel motion or crosshead. The other end of the beam is connected to a disk crank. The crankshaft has a 34mm diameter machined brass flywheel. The centre of the crankshaft appears to be running in a miniature ball race.