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Although this is almost certainly Frullania F. dilatata is not the only species which grows on trees. To be sure which you have got you need to check the shape of the upper and under leaf lobes, and the presence or absence and distribution of modified cells in the upper leaf lobe. You can see all of this with a x20 lens. See the BBS Field Guide for details.
I remember which tree it is so will have another look on my next dog walk....
Lat/Lng: 51.0822, 0.0357
OS grid ref: TQ426334
Very approx location