Another (probably) not-exceptionally-difficult Jumbo.
As always, * indicates an anagram.
| Across |
| 1 | REFECTORY - alternate letters of bEeF, in RECTORY |
| 6 | SHOW-OFF - SHOW, + OF F |
| 10 | ORIEL - OR + IE + L |
| 13 | SURREPTITIOUS - SURREy, + PIOUS around TIT |
| 14 | ON THE SPOT - double definition |
| 15 | HEELTAP - HE + E +LT, + pa (reversed) |
| 16 | TWELFTH - priesT, + (left)* in W + churcH |
| 17 | GRIMACE - AC in GRIME |
| 18 | PAMPHLETEERS - P in (team helpers)* |
| 20 | INTERNSHIP - IN + TERN'S + HIP |
| 23 | JUNTA - JUN (short for June) + TA |
| 24 | SEED PEARL - SEE EARL, around D + Purchase |
| 25 | SHE-BEAR - SHE (the H. Rider Haggard novel) + BEAR. "Rupert's mother" refers to the long-running UK cartoon strip for children |
|
| 26 | CITY SLICKER - (cricket is lowkey)* |
| 28 | CHRONOMETER - on mantelpiece in (the corner)* |
| 30 | SIGHT-READER - READER ("senior lecturer") after SIGHT |
| 32 | UNNATURALLY - UN, + LadY after NATURAL |
| 34 | ROADBED - ROBED around AD |
| 36 | NOTORIOUS - NOT US, around O + RIO |
| 38 | IMPEL - IE around MP, + L |
| 39 | WISHY-WASHY - (why his way seems)* |
| 41 | STRONG-MINDED - MINDED after STRONG |
| 45 | PROGRAM - PRO + G + RAM |
| 46 | BUTTERY - UTTER, in B + Youth |
| 47 | SHARPEN - HARP in SEN |
| 49 | DESPERADO - DES + ADO, around rep (reversed) |
| 50 | AUDACIOUSNESS - A + U, + cad (reversed), + NESS after IOUS |
| 52 | EASED - E + AS ED[itor] |
| 53 | DUKEDOM - Distinguishing + UK, + mode (reversed) |
| 54 | OBSTINACY - OB (Old Boys), + TINY around AC |
| Down |
| 1 | ROSE-HIP - or (reversed), + SHIP around E |
| 2 | FORGET-ME-NOT - TOT around MEN, after FORGE |
| 3 | CLEFT - CLEF + collectT |
| 4 | OCTUPLE - (couple + abouT)* |
| 5 | YET - Trust after YE |
| 6 | STONECROP - STONE, + COP around caR |
| 7 | OSSIFY - hidden in crOSS IF You |
| 8 | OTORHINOLARYNGOLOGY - (on orgy looting royal hospital)*. The beauty of a Jumbo puzzle is that it can include lovely 19-letter words like this! |
| 9 | FATIGUE - FAT + GUy, around I, + E |
| 10 | OBEDIENCE - ONCE, around BEDE around I |
| 11 | IMPEACHMENT - I'M PEACH, + MEN + Taking |
| 12 | LATTE - LATE around T |
| 16 | THE NEW KID ON THE BLOCK - THE NEW KID (both Billy and KID refrrring to goats), + ON THE BLOCK |
| 19 | HEADSET - HE + SET, around AD |
| 21 | PORTRAYAL - RAY in PORTAL |
| 22 | MANCHU - hidden in RoMAN CHUrch |
| 23 | JACK SCREW - JACK + SCREW |
| 24 | STIPEND - TIro in SPEND |
| 25 | SONATAS - SON + AT + Abingdon School |
| 27 | RARITY - RAT + Y, around RI |
| 29 | MARTINI - MART + IN + I |
| 31 | GLASSHOUSES - double indication |
| 33 | LEPIDOPTERA - (dire to apple)*. At the risk of seeming pedantic (oh all right then, I admit it, I'm pedantic!), the LEPIDOPTERA are an order of insects, not a class of insects - they're part of the class Insecta |
| 35 | BOYFRIEND - FRIEND (member of the Quakers or Society of Friends) after BOY ('my' here indicates an exclamation) |
| 37 | ROTTERDAM - R + OTTER +DAM |
| 40 | ARMBAND - ARM + B + AND |
| 42 | GASEOUS - Employed Only, in GA + S US |
| 43 | DYNASTY - DodgY + NASTY |
| 44 | STRAND - double definition |
| 45 | PADRE - PAD + RE |
| 48 | ASSAI - A + S + S + AI |
| 51 | COO - double definition |