10a Perhaps pen letters in Athens describing the empty pasty (4,4)
25a Brief pint drinking Queen and Country (6)
27a What drug pusher may say at entrance "sweet dreams" (6)
8d Arrangement with cheap horn for Spooner (6)
16d Largely unadorned little Italian church? Actually, for starters, it's anything but! (8)
10a Mute Swan = a pen is a female swan. Mu's (greel letters) around te (the without the middle letter) + wan (pasty)
25a Belize = Liz in "bee(r)
8d Syntax = tin sax
16d Basilica = basi(c) L(ittle) I(talian)c(hurch) A(ctually)