How do I solve 12 across in Times Cryptic 29549?

Question

Accepted Answer

12 across reads "Prominent speech in support of London Transport" (11 letters); the answer is PROTUBERANT. It's a charade: the answer breaks into parts in clue order, each part clued by a word or short phrase. No indicators needed; watch for standard abbreviations (RA = artist, US = American, IN = at home) and short synonyms. The full step-by-step breakdown is on this page.

Prominent speech in support of London Transport (11)

12A — Prominent speech in support of London Transport (11) — PROTUBERANT