Hi,
Project with title "UK Speakers Voice Recording Project 11" just appeared on my screen and i red your description "We are looking for British English native speakers that can record four 15-minute conversations with......"
I am apt photoshop artist with skills including Audio Services, Anything Goes, English (UK) Translator, Audio Production and Voice Talent.
Seems like your are on the right place and i am the right person offering services for this, i have recently done similar project which you can check on this link:
https://www.freelancer.com/u/LetsDezign.html
Do you have any specific required dimensions ?