Confidence: It's likely to be this, but I can't be certain.
Notes: This is quite tricky. A number of the lobe endings appear to be hooded, which would point to P. ascendens, but where we can see soralia, they are on lobe tips that have turned back - diagnostic of P. tenella. Sometimes hooded lobe tips can split to produce "tenella-like" soralia, but not, I think, to the extent shown here. Both species are variable (and some doubt they are really distinct). On balance I think this is rather exuberant P. tenella, but 'gardener' or others are welcome to disagree! Alan