I remember reading an article by Colin Terris about how Paul had showed him a double Harlequin, and after a suggestion from CT went off and made a Triple one... - if I'm recalling correctly - I'll need to go and hunt down the article and confirm later.
Given that this does not use a normal CG ground (Peat, heather etc hot melt), and does not look like a Harland era ground to me, (tho no expert)
- i'm wondering if this is a trial piece of Paul's c1970, using his crushed/frit glass ground, and a bridge piece between his original single harlequin and an evolving double harlequin design?
Both his single and double Harlequin designs were released to CG in 1971 I believe, first appearing in the 1972 catalogue.
The Double harlequin became a much taller dome design in production.
Other possibilities include:
1) an apprentice's trial piece, rejected, sold in the CG factory shop - although would normally have been marked CIIG on the base, not all were.
-or could have been polished off....
.. but it should have had a CG cane in it post 1975, if intended to be a sale piece if it came out OK. - but still the wrong ground....
2) possibly a David Hurry piece? I know David produces fish weights and others in the late PY Harland style - you can see them on his web site.
-but don't know if he ever emulated harlequins.
My bet is that it could well be an early PY trial piece, sold in the CG shop. UV testing needed?
Just in case it is a PY trial piece -I suggest you don't sell it, but wait and see what other info may appear to confirm or deny this possibility.
Perhaps if you live near Kev H he could do a UV test on it for you?