A company is considered dormant if it doesn't trade and has no ‘significant accounting transactions’ during an accounting period. Dormant companies may be registered to hold a company name or for various other reasons. Dormant companies must still file annual accounts.
As long as a company isn’t dissolved, it’s obliged to submit company accounts. A dormant company must submit a balance sheet and any relevant notes to the accounts. Any transactions performed will mean filing full accounts to Companies House.