Topper was a stencil name...this is a Conn Pan American, so their second line horns. Not to be confused with their Naked Ladies. So it's a "PanAm stencil".
Not much market value here in states maybe $100usd in that condition. Might be worth a tad more on your side of pond. 125quid maybe, tops ?
The serial number, which looks like 60086 ?.... will not conform to Conn serial numbers, Pan Americans (although made by Conn at their plant, that is what they called their second shelf line) had their own serial sequence.
Kevin McKnight (member Badenia ofver at SOTW not sure if he is a member here ?) put together that serial number list over a period of about 5 years, I helped him with the registry a little bit, so it's an accurate list...