1d Plymouth's a European city [4] p??a pisa?
5d strange invention, note at first [5] a?i?n alien?
11d its covering everything up, that's plain [5] l?a?o llano?
17d loud noise can end a glower [5] f?o?n frown?
Thanks dannyk. I think you mentioned the increased use by setters of using an initial letter. I don't really see why Plymouth would be P. The postcode is PL. Is it to do with car reg nos or something else?