I've followed [this blog][1]
[1]: https://blogs.technet.microsoft.com/anneste/2011/11/02/how-to-create-an-infopath-form-to-auto-populate-data-in-sharepoint-2010/ which works like a dream.
It populates an email field with my email address but what I what to happen is that a user selects someone using a people picket field and then fields are populated with that persons details.
Any idea how I could achieve this? Thanks