HELP - When is a company considered part of a group for Companies House and Audit purposes?

Hi All,

Probably quite a simple question, but I obviously want to get it right.

When is a company considered part of a group, particularly for Companies House and Audit exemption purposes.

I know that the 'parent' must have control for Associated companies rules in Corporation Tax.

Would a company with 25% or 30% of the share capital be considered part of a group for Audit exemption purposes?

I hope you can help as soon as possible.

All the best.

David