Another strange one! The frame is built from a Chater Lea lug set, which means it could have been assembled by any bicycle shop or motorcycle manufacturer - anyone with the ability to braze tubes into lugs. The Chater Lea spring fork fitted was listed in their 1907 catalogue and the "low" frame (with the top tube attached low to the steering head, which is braced at the top) was adopted out here in Australia for 1908. The rear stand is a commonly-used type of the period, while the back carrier and toolbox might be best forgotten.
But aren't the matching torpedo-style tanks lovely! That said, the location of the oil tank and hand pump wouldn't be the best in a spill...
The motor has me beat. The inlet valve is over the exhaust, and is either atmospheric or operated by a push rod and rocker (can't quite see). Unusual for a British machine of this period, but not uncommon on the continent or in the USA. (Not Minerva, however, as they went to side valves very early.) The engine looks fairly "modern" - it could be contemporary with the cycle parts or even later. The front engine plates look a bit amateurish, as if the motor could have come from elsewhere, and the chain-driven magneto at the front and the carby would be part of on-going modernisation.
If Rob's grandfather was a mechanical-type-guy, I'd say this is his constantly-evolving-dream-machine.
If Rob has a strong light and a magnifying glass, he might be able to read the name on the tank, which I fancy I can see written in upward-slanting script directly below the oil pump.
Leon