They say P. germanica is less spotted on wings than P. communis. But the best characters are the male genitalia. Female genitalia also differ, if only you can examine them. You can see some images of communis and germanica on these pages. Your specimen looks to me more like those presented on those pages as communis. Given that germanica is also much rarer in Britain, I would say that P. communis is a more likely ID for your fly.