Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
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It's so annoying that it is impossible to correct a typo in the notes to an identification, even though one has to type them into a tiny little box that does little to help proof-reading.
So for "do do", read "do not"!
My interpretation of "lirellae opening widely" vs. "not opening widely" in Dobson's key has probably sent me off course here. I did look at both routes, but "thallus brown" put me off O. vulgata/niveoatra/lithryga. The full text ("thallus grey or brown") is far more helpful.
It looks like I will have to relive the joy of sectioning these fiddly apothecia to measure ascospore width - not because I disagree, I hasten to add, but simply to satisfy myself (and as punishment for not measuring width the first time around).
Edit: spores re-examined and found to be 6-7µm wide. All in the sample were 5-septate. So, apparently O. varia after all.
I have to say I am surprised at the microscopic characters, as the lirellae are not so widely open as I expect in O. varia, they are more elegant (whatever I mean by that), and the Lichens of Great Britain and Ireland account states, "apothecia ... infrequently branched, rarely stellate."
Generally, reliable published photographs match my undersatnding of a less "elegant" lichen, though that in Holien & Tønsberg is perhaps not too far away.
Perhaps, though, looking at your photograph again, the lirellae are clustered in a stellate manner rather than truly stellate?
Of course, O. varia doesn't get its name for nothing and it may well be a composite species. In view of the spore width I have to agree this is most likley O. varia - not really a lot of choice. So, with some reluctance, I am adding agreement to your original ID.
Another look at the sample (the protruding chunk of bark in the first photo) reveals that many of the apothecia are clustered but discrete, though several are branched or stellate. Photos appended.
The nearest comparable images I can find are here and here, but I gather from what you have said that this is more typical.
I thought these lirellate lichens were going to be a challenge!
Lat/Lng: 54.0015, -1.8988
OS grid ref: SE067561