Voiceover for e-learning course

I'm looking for british accent female voicover for training course for Early Years workers. The current version is around 3 hours in total in recording, however we are updating it and it might little bit more. Approximately 40-60000 words. Will know exactly once the rewriting is completed. It would be ideal if the voiceover had access to video recording with green screen as we would love the introduction and summary be done as a video.