I tackled this on a sunny afternoon under "exam conditions" and was surprised to find I had finished it just with the 20 minutes, with all parsed, although 4d and 6d were from wordplay alone until I checked them afterwards. The long clues at 1a and 28a went in quickly, making the rest easier. No doubt you brave contestants in London were lulled into a sense of unwarranted optimism; I suspect the next few are not so gentle. It seems they're coming along every Wednesday so I have the short straw. Apologies to those who already sat the exam.
| Across |
| 1 | DO ONES LEVEL BEST - DOONE'S = Lorna's, LEVEL = flat, BEST = second to none; D make the maximum effort. |
| 9 | LETTING ON - DD. |
| 10 | CLUNG - C(ONSERVATIVE), LUNG = organ; D held on. |
| 11 | AGORAS - AGO = previously, RAS(H) = reckless, curtailed; D Greek markets. I'd have thought the plural of agora should be agores, but apparently not in English. |
| 12 | MATERIEL - MATE = ally, R = end of war, I E - that is, L = left; D military stuff. A French word adopted into English for this meaning only. |
| 13 | DIETER - DETER = put off, stuff in I (end of salami); D &lit. |
| 15 | TOUCHING - DD; moving as in emotional, on as in 'in contact with'. |
| 18 | BROUHAHA - BROU sounds like BREW = plan, cook up. HAHA = laughter. D uproar. Curious, I looked up the etymology, which is doubtful, beyond the French; possibly from Hebrew words to do with noisy welcomes. |
| 19 | STONED - I see this as STD for standard, insert ONE for joke, as in 'you are a one'; D wasted. |
| 21 | SPINSTER - PINS for skittles, inside STER(N) for endlessly demanding; D she's unmatched. |
| 23 | DARKEN - (N)ARK = nameless informer, inside DEN = retreat; D dim. |
| 26 | IVORY - OR = gold, inside IVY = climber; D tooth. |
| 27 | DUNSTABLE - D for DUKE, UNSTABLE = not firmly settled, D English town. In my haste I first put in D ON CASTER thinking on a caster would be unsettled, but the checker from 24d made me think again; the right answer is better. |
| 28 | TOSSING THE CABER - (SCOTS HATE BEING)*, R = introduction of Rare; D Highland fling. Nice and easy. |
| Down |
| 1 | DULLARD - LUD = lord, as in M'Lud; sent up = reversed; LARD = fat; D stupid. |
| 2 | OUTDO - OUT = available, DO = make; D best, as in beat. |
| 3 | ELIZABETH - Port Elizabeth in South Africa; Elizabeth David, superb cookery writer (French Provincial Cooking remains a classic); DD. |
| 4 | LOGE - LOG = tree trunk, E = eucalyptus primarily; D box, a loge is a private box e.g. in a theatre. |
| 5 | VINDALOO - VINO for wine, insert O LAD (old boy) reversed; D hot dish. |
| 6 | LUCRE - Insert R (last for eveR) into LUCE (alternative name for a pike); D tin, money. |
| 7 | ERUDITION - Insert RU (game) into EDITION (version); D learning. |
| 8 | TAGALOG - TAG (label) A, LOG (record); D Asian language. I spent a week diving in the Philippines once, and never understood a word of Tagalog, but it sounded nice. |
| 14 | EMOTICONS - (ECONOMIST)*; D smileys, for example; ☺ ☺ ☺ |
| 16 | CATHARTIC - CATH is the lady, ARTIC(ULATED) lorry, D effecting release. |
| 17 | SHEEPDOG - (SPEED HOG)*' D one could redirect. |
| 18 | BASSIST - B(ook); ASSIST = second; D musician. |
| 20 | DANSEUR - (SUNDAE)*, R for right; D Pavlova's partner. |
| 22 | STYLI - STYLIST is the hairdresser; remove the second ST; D needles, e.g. once used in record players. |
| 24 | KEBAB - BABE = gorgeous girl, add K for king; flip to reverse; D dish. |
| 25 | INCH - Hidden word in plaIN CHocolate; D small amount. |