Do side panels, and top panels get checked in the same way as a fire door by door manufacturers? If so, what type of certification do they get?

If they don’t, how do you confirm the fire rating of these panels?  Would they have a CE mark or equivalent?

Side panels and over panels for fire resisting doors can be of solid timber or glass, both are subject to a fire performance test or fire resistance assessment report.

Solid timber panels would be made from the same core or blank as the door leaf - refer to the technical data for the particular door in question. 

With regard to glazed panels - the glass manufacturer will possess data to demonstrate fire resistance performance when used with a particular timber-based door type / door frame panel / glass retention system.  This guidance document may be useful  https://www.ggf.org.uk/publications/fire-resistant-glazing-publications/guide-best-practice-specification-use-fire-resistant-glazed-systems/

Currently in the UK, internal fire doors may not be CE marked.  

Thanks for this Neil.

I take it then panels would have FR label or plug the same as a door. Or do they come with UKAS/UKCA information?

The panels could be third party certificated as part of a fire door-set, in which case the complete door-set would carry a certification scheme label or plug.  But they don't have to be, working in scope of the evidence of fire resistance performance for the door is sufficient to achieve compliance to BS 8214.