Great Britain £10 Strip-of-5 #1478 Used On Piece

The paper has fluorescent fibers, and they light up around 'ten pounds', but not around 'L10'. Is that a good thing?

Interesting. These have the tagging around the crosses, so 2A. A quick check of my singles shows this may be the surest way to tell, since there is not even a trace of tagging around the crosses on 1A. The tagging on '£10' (I found the '£' on this little machine!) seems to come in the range of full-on to almost not, to not at all. Almost subjective. Also, the shields on this strip barely light up at all, more white than any shade of yellow or green like yours. Scott mentions water damage possible, but these have seemingly never known the kiss of water. 

Unfiltered longwave black light, not sure of the exact range. When you said 'fluorescent', that was the lamp I reached for. I have several different shortwave lamps, I'll check with those a bit later.

My sample looks like the above sample with the ten pounds and the shield. I do not see a separate catalog number in SG concise but it does mention it. Mine is off paper and no gum.

Scott catalog has been called a worldwide generalized catalog so that is why they do not have Great Britain phosphor issues listed yet they do list a variety of the above as 1478a with silver (Queen head missing) at $1750. Anyone seeking that is not a generalist.

The 2018 SG Concise does list the missing silver variety at £5000.