Schools get bombarded with leaflets, flyers and emails from many people and organisations offering to provide PSHCE related speakers, workshops or staff training. Over more than a decade of working in schools I have heard from teachers of varying degrees of success with outside speakers.
I have collated a list below of speakers and organisations I either know personally or have heard excellent feedback on from schools I visit.
The McLellan Practice http://mclellan.info
All about Sex & Relationships Education http://www.allaboutsre.co.uk/
Angela Findlay - Talks on Arts in Prison
Shaun Attwood - https://shaunattwood.com/shaun/drugs-and-prison/