Solution to 22A has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Deteriorated in speech in 10 years (6) DECADE (~decayed)
4 Say, transport cat in mat (6) CARPET {CAR}{PET}
9 Ingredients in muesli, milk are insufficient (4) SLIM [T]
10 Pastor's feeling bitter about offering (10) PRESENTING {P}{RESENTING}
12 Tied up a new thief in Delhi, held every second (8) ANCHORED {A}{N}{CHOR}{hElD}
13 Join volunteers in treat (9) ENTERTAIN {ENTER}{TA}{IN}
15 Good points on birds (5) GEESE {G}{E}{E}{S}{E}
18 Two characters substitute each offer to get dressmakers as clients (9) CUSTOMERS {C)-o+u)UST(-u+o)OMERS} each offer or each other?
22 Brussels' tie with one at Norway? No, it's Danish, perhaps (8) ?U?O?E?N ()
23 Tour without pressure, fly perhaps (6) INSECT INSpECT
25 Companies have function in public transports crossing limits at the terminus (10) {BU{SINE}SES} over {l...tS}
26 One time in elders' house there were rodents (4) RATS {R{A}{T}S}
27 Companionless ladies surround single with ponytail (6) LONELY {L}{ONE}{L}{ponY}
28 Doctor stays behind small yard having sold perimeter away to Mark (6) SYMBOL {MB}<=>{S}{Y} and {sOLd}
DOWN
3 Store in store? Yes in Spain, set inside (7) DEPOSIT {DEPO{SI}T}
5 Department in New York seizes cocaine after a great engagement at the front (6) AGENCY {N{C}Y}<=>{A}{Great}{En...t}
6 Convert rupee to ml of fuel (9) PETROLEUM*
7 When females becomes tense filters become passages (7) TUNNELS (-f+t)TUNNELS
8 Auntie's scones are prepared with perseverance (13) TENACIOUSNESS*
14 Once poison is administered after injecting some lead, it will be an outbreak (9) EXPLOSION {EX}{POISON+Lead}*
17 One French-American seen with unionist gangster which is rare (7) UNUSUAL {UN}{US}{U}{AL}
19 Longing for a number featuring Sinead O' Connor primarily (7) THIRSTY {THIR{Si...r}TY}
20 Report? Article is being rewritten (7) RECITAL*
21 Say, Rice's first conflict on East is bona fide (6) CEREAL {Co...t}{E}{REAL}
24 Supreme Court obstacle for Bush (5) SCRUB {SC}{RUB}
Reference List
Pastor = P, Street = ST, Square = S, New = N, Thief in Delhi = CHOR, Volunteers = TA(Territorial Army), Good = G, Points = E,S, Prince = P, Pressure = P, Time = T, Elders' house = RS(Rajya Sabha), Lady = L, Small = S, Yar = Y, Charlie = C, Henry = H, Society = S, Yes in Spanish = SI, Cocaine = C, Females = F, Tense = T, One in French = UN, Gangster = AL(Capone), East = E