A range of videos and articles are available on the Legal Island Hub that deal provide guidance on what mediation is; when to use it and who should mediate.  Here is a selection:

Mediation Video Series

In this video series Dorcas Crawford, discusses the various elements of workplace mediation.

• Why Workplace Mediation Works
• The Parties’ Role in Workplace Mediation
• The Neutral Mediator – What Neutrality Means and What it Entails
• How to Embed a Mediation Culture into Your Organisation

https://www.legal-island.com/employment-law-hub/regular-features/workplace-mediation/

What does mediation involve and are there any drawbacks?

Seamus McGranaghan, O’Reilly Stewart Solicitors discusses the pros and cons of mediation.
https://www.legal-island.com/articles/uk/features/discussion/2018/may/mediation-any-drawbacks/

Who needs a mediator anyway?

This is a common question, as people try to understand the distinctions between terms such as mediate, conciliate, facilitate, or simply advise? At the core of the decision to engage a mediator is always a wish to find a solution to what the parties determine is, in some way, an intractable issue. I think a good description as to what a skilled mediator brings is “Any process for resolving disputes in which another person helps parties negotiate a settlement.”  Steve Tweed of &|Ampersand discusses what a mediator does and who needs them. 
https://www.legal-island.com/articles/uk/features/hr/2017/nov/who-needs-a-mediator-anyway/

What sort of Mediation do you want?

Mediation comes in many forms, some more successful than others.   Steve Tweed, of &|Ampersand discusses a number of mediation options.
https://www.legal-island.com/articles/uk/features/hr/2017/sept/what-sort-of-mediation-do-you-want/

Independent third-party mediation - alternative approach for managing reorganisation

This article reflects on a case study in which independent third-party mediation is employed as a successful and timely alternative to traditional approaches used in managing reorganisation. This case study demonstrates how mediation can be used to avoid a potentially costly and damaging dispute.
https://www.legal-island.com/articles/uk/features/hr/2017/sept/independent-third-party-mediation-alternative-approach-for-managing-reorganisation/