A dormant company is a company that is not actively doing business or trading and does not have any other sources of income, such as investments or tangible assets. According to the Companies Act 2006, a company is considered dormant if it has no significant accounting transactions (transactions required to be recorded in the company's accounting records under section 386 of the Companies Act 2006). For more information, please follow the link 

https://www.legislation.gov.uk/ukpga/2006/46/section/1169 

When determining whether a company is dormant, certain financial transactions may be disregarded, including payment for shares taken by subscribers to the memorandum of association, fees paid to the Registrar of Companies for certain changes or filings, and penalties for failure to deliver accounts.

• Submit the confirmation statement to Companies House on time.
• Submit the company's year-end accounts to Companies House by the deadline.
• Exercise independent judgment to determine if the company is dormant for Companies House and inactive for corporation tax purposes.
• There are other responsibilities that apply to trading companies, such as acting within powers, promoting the success of the company, exercising reasonable care, skill, and diligence, avoiding conflicts of interest, not accepting benefits from third parties, and declaring interests in proposed or existing transactions or arrangements with the company.

• If your company does not have a business bank account or if no bank charges have been paid during the year.
• If no expenses have been paid for the company other than Companies House fees.
• If accountancy fees are paid by the director personally and are not recorded as the company's accounting transactions.

The authentication code for Companies House is a unique code issued to companies registered in the United Kingdom for authentication and online filing purposes. Each company has its own authentication code, which is typically sent by mail to the registered office address of the company upon incorporation. It can also be obtained by filing certain forms or requesting it directly from Companies House. To obtain the authentication code for a specific company, you should refer to the official correspondence or documentation received from Companies House or contact them directly for assistance.