Jam sugar contains added pectin. But I can't see anywhere how much. Preserving sugar, on the other hand doesn't. It just has large quick dissolving crystals. Confusing, isn't it? Jam sugar and preserving sugar

If it is a UK recipe the chances are high that it is not intended to be canned so it might not pass muster in the US. Maybe if you post it people here can tell you if it is likely to be considered safe?

Recipe is basically apple jelly with spices, sugar. I'll use the NCHFP or BBB for recipe and add the spices and lemon juice and leave out the pectin as most apple recipes don't need it, cook to gel stage, then BWB for 10 min in sterilized jars.

rosemary pairs well with apples, so bay leaves might also.

Apples are high-pectin anyway, so I agree added pectin shouldn't be necessary. Jam sugar is (by weight) 98% sugar and .7% pectin. There's also some citric acid and sometimes preservatives, accounting for the remaining 1.3%. (German jam sugars come in 3 strengths, so that's a whole different issue.)

Basically UK jam sugar presumes a traditional 1:1 ratio of fruit to sugar.

As far as safety is concerned, truthfully with few exceptions, jams and jellies don't have to be canned. They're high-acid and the sugar binds any water which might cause an issue. Canning full-sugar preserves principally offers longevity.