Tarmac colonists

My morning's walk today took me along Becketts Close and I was surprised to note the extent to which lichens have colonised the tarmac there. The species involved appears to be Lecanora campestris, a very common lichen which thrives in this situation. I have identified about 20 lichen species around Byfield but crustose lichens such as the one in question can be very tricky to identify. (A further examination showed this species to be Lecanora muralis.) Light trampling appears not to bother it and in fact small fragments of the thallus may be broken off and help with the colonisation process. I must bring home a sample and try to obtain a positive identification