UK GDPR and Data Protection Act 2018: Data protection legislation governing the processing and sharing of personal information in the UK. Critical for ensuring compliant handling of personal data when authorizing someone to speak on behalf of another.

Mental Capacity Act 2005: Key legislation that ensures the person giving consent has the legal capacity to make decisions. Sets out the framework for assessing mental capacity and making decisions on behalf of those who lack capacity.

Powers of Attorney Act 1971: Fundamental legislation governing the creation and execution of powers of attorney, which may be relevant to ensure the letter of consent doesn't inadvertently create broader authority than intended.

Lasting Powers of Attorney Regulations 2007: Regulations governing lasting and enduring powers of attorney, important for understanding the boundaries between a simple letter of consent and more formal power of attorney arrangements.

Common Law Agency Principles: Legal principles governing relationships where one person (agent) acts on behalf of another (principal), fundamental to understanding the legal framework of speaking on behalf of another.

Contract Law Fundamentals: Basic principles of contract law that ensure the letter of consent is legally valid and enforceable under English and Welsh law.

Financial Services and Markets Act 2000: Relevant when the authority to speak involves financial matters, ensuring compliance with financial services regulations.

Access to Health Records Act 1990: Applicable when the authority to speak involves healthcare matters, governing access to and disclosure of health information.