This Practice Note examines deceptive design practices in online choice architecture (OCA), focusing on techniques such as dark patterns, dark nudges, and sludge. It covers the impact on consumer choice and competition, alongside the legislative framework in the UK, including the unfair commercial practices (UCP) provisions of the Digital Markets, Competition and Consumers Act 2024 (DMCCA 2024). Techniques discussed in this Practice Note are typically incorporated into business-to-consumer (B2C) websites, apps and other technology platforms. OCA refers to the design features and elements within digital environments, such as websites, that influence how users make decisions. This may include the presentation and placement of choices (such as ‘buy now’ buttons), the design of interfaces, and the use of algorithms to personalise experiences. In many instances, OCA has a beneficial impact on consumer choice and assists consumers to navigate platforms effectively. However, when it is designed to intentionally manipulate, mislead or pressure a consumer, this may be referred to as a ‘dark pattern’, ‘dark nudge’ or ‘sludge’ technique and constitute a breach of consumer protection,