Are a spouse's or relative's companies associated?

When family members' companies count as associated for corporation tax, which relatives count, and what HMRC means by substantial commercial interdependence.

Updated 1 November 2026. General guidance, not tax advice.

Check a company

Enter a company name or number to see its ownership and likely associated companies.

A company owned by your spouse, parent, child or sibling isn't automatically associated with yours. Their shares are only added to yours when the two companies are substantially interdependent: linked financially, economically or organisationally. Without those links, each family member's companies are judged on their own.

The starting point: control

Two companies are associated if one controls the other, or both are controlled by the same person or group of persons. Control generally means more than 50% of the shares, the votes, the rights to income or the rights to assets on a winding up.

So if you own 100% of one company and your spouse owns 100% of another, the first question is simply whether one person, or one group of people, controls both. Here nobody does, so the companies aren't associated unless the family rule below applies.

If family members own shares in both companies, look at their holdings together as a group. For example, if you and your brother each own 50% of two companies, the two of you together control both, and they are associated whatever the family relationship.

When a relative's shares are added to yours

When testing control, the shares and rights of a person's associates can be treated as theirs. For associated companies, though, an associate's rights are only added where there is substantial commercial interdependence between the companies.

Your associates include your:

husband, wife or civil partner
parents, grandparents and earlier generations
children, grandchildren and later generations
brothers and sisters
partners in a partnership you're a member of
trustees of a trust you or a relative set up, or of a trust holding the company's shares that you benefit from

Uncles, aunts, cousins, nephews, nieces and in-laws (other than your own spouse or civil partner) aren't relatives for this purpose.

The rights of someone's nominees always count as theirs, interdependence or not.

What substantial commercial interdependence means

HMRC looks at three kinds of link. The companies don't need all three, but the links must be substantial.

Financial links, for example:

one company gives financial support to the other, directly or indirectly
both have a financial interest in the same business

Economic links, for example:

the companies pursue the same economic objective
the activities of one benefit the other
they have common customers

Organisational links, for example:

common management
common employees
common premises
common equipment

HMRC's examples

HMRC's manual works through examples. Ones that point to no association:

One company rents premises from the other at a market rent, with nothing more.
A father personally guarantees his son's company loan, and the father's own company gives no support or security.
A wife lent her husband the money to start his company, secured on her own company's assets, the loan was repaid, and no other links remain.
Husband and wife run separate companies in the same trade, with no links between them.
Two companies are run from the family home, sharing the household phone line for occasional business calls and internet access.

Ones that point to association:

Two companies share premises, staff and customers, and each benefits from the other's activities.
One company is the exclusive supplier to the other, and they share customers.
Two companies split from one family business still share facilities, staff and equipment.

Every case turns on its facts, so record what links exist, and don't exist, between the companies.

Checking the companies

The public register shows who owns each company but not family relationships or how the companies trade with each other. When you check a company, possible family links, such as the same surname and service address, shared directors or a shared registered office, are listed as Please check. Answer the question for each one and the count updates. Nothing is counted on a guess.