Persuasiveness in oral communication in English can be expressed with various vocal phonetic cues that may not be readily accessible to English second language (L2) learners whose native language may employ a different set of cues. With a goal to increase L2 learners' perceived spoken confidence and persuasiveness, and obtain empirical evidence for phonetic adjustments that native English speakers make to influence listeners, the current study explored the use of consonant prolongation in stressed syllable onsets for emphasis by native British English speakers and English L2 learners. The native speakers' durations of continuant consonants and voiceless stop consonant voice onset times (VOTs) in (1) neutrally-produced speech and (2) persuasively delivered motivational/shocking/emotional messages were compared to Latvian L2 English speakers' productions. The results revealed that in persuasive speech, the British speakers' consonantal durations, particularly those of continuants, got significantly longer relative to the vowels that followed them; for English L2 learners, the duration of consonants did not change as a factor of speech type. This is in line with our previous research with American English speakers and carries implications for L2 speech learning and teaching.