I'm based in the UK and don't know anyone who can be my mentor. What should I do?

In the UK, there should be a Fellow or Registered Member living or working reasonably close to you who you could approach. You start by making contact with other IEHF members, perhaps by attending the Annual Conference or by joining a Regional Group or Special Interest Group, and by keeping in contact with other ergonomists you meet. If all else fails, the Institute office may be able to help by identifying other professional members that you could approach.