Hi
Guidance on when you lend your company money is available at
Director's loans: If you lend your company money.
Guidance on loan relationships is available at
CFM30000 - Loan relationships: Contents - HMRC internal manual onwards.
Not all pre-incorporation costs can be claimed. For example, you cannot claim the one-off company formation costs associated with incorporating your business as this is regarded as a capital expense. Please refer to guidance at
BIM46351 - Specific deductions: pre-trading expenditure: scope - HMRC internal manual
Whilst you aren't legally required to use an accountant, completing accounts for a limited company can become complex. It's one of the considerations you need to make before setting up a limited company.
Corporation Tax is a regime based on self assessment. HMRC doesn’t offer an accountancy service or tax planning advice.
If after referring to all available guidance and relevant legislation, you are unable to complete the company accounts, computation and tax returns, please seek advice from an accountant.
Your question regarding a written agreement is possibly more appropriate to Companies House or even Company Law.
Sorry we cannot be of more help with this.
Thank you