Solution to 27A has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
8 Molten rock from volcano in Shangri-La valley (4) LAVA [T]
9 Anglian run goes around circle in the wood (6,4) ANNUAL RING*
10 Ancient city state at that time located amid the western boundaries of Aegean Sea (6) ATHENS {Ae...n}{THEN}{Sea}
11 Descent from perigee, turning around beginning of downfall (8) PEDIGREE {PERIGEE}* over {Do...l}
12 Inflated invoice due (8) BILLOWED {BILL}{OWED}
14 After 5, inane to go about in Austrian province (6) VIENNA {V}{INANE}*
16 Game available in Honolulu dormitory (4) LUDO [T]
17 Saint is safe (5) PETER [DD]
18 Droop with love for starchy food (4) SAGO {SAG}{O}
19 Boy is at the front of winding line around last bunker in one time walled city in Europe (6) BERLIN {B}{LINE*} over {b...eR}
21 Take away card from chambermaids working for wife of British official in India (8) MEMSAHIB cHaMBErMAIdS*
23 South African country's bird enters sailing boat (8) BOTSWANA {BOT{SWAN}A*}
26 Noise about tailless bull running around in capital (6) DUBLIN {D{BULl}*IN}
27 In other words, Christian Era for advanced age, informally (4,6) ?N?O ?O?I?I (Addendum - ANNO DOMINI [DD] - See comments)
28 Flower is small and yellow at first (4) LILY {LIL}{Ye...w}
DOWN
1 Let tsunami flow for final 60 seconds (4-6) LAST MINUTE*
2 Extraordinarily alert in court and site of famous battle (8) WATERLOO {W{ALERT*}OO}
3 After fight, observed city in Poland (6) WARSAW {WAR}{SAW}
4 Cut rejected pins (4) SNIP <=
5 Deliver Chinese port (4,4) HAND OVER {HAN}{DOVER}
6 Prince gets fever in city (6) PRAGUE {PR}{AGUE}
7 Wager in Dantewada (4) ANTE [T]
13 A particular piece of information: "Wrongly amputated after removing tape" (5) DATUM AMpUtaTeD*
15 Manipulate EEG billing to make it insignificant (10) NEGLIGIBLE*
17 Military headquarters shifting to Penang? (8) PENTAGON*
18 Steel bat bent into safety device (4,4) SEAT BELT*
20 Student is fine in French and Portuguese city (6) LISBON {L}{IS}{BON}
22 Massachusetts Democrat gets free capital (6) MADRID {MA}{D}{RID}
24 Admits. "Wrongly won by son" (4) OWNS {WON*}{S}
25 Strain at the heart of sectarianism (4) ARIA [T]
Reference List
Boy = B, Chinese = HAN, Prince = PR, Student = L, Fine in French = BON, Democrat = D, Son = S