This thesis analyses the competitive aspects of bank merger transactions under the law of the United Kingdom ('UK') and the United States ('US'), including the applicable law of the European Union ('EU'). This thesis, also, covers bank mergers and competition in view of the financial crisis 2007-08 that is known as the Global Financial Crisis ('GFC'). The analysis under UK and EU law focuses on competition issues in the banking and financial sector, notwithstanding that competition laws in these jurisdictions apply broadly to all sectors of the economy. The US law analysis is based on competition law from federal antitrust and bank regulatory authorities, case law, as well as consumer protection regulation. This thesis establishes a comparative framework for understanding the competition provisions, examination methods of mergers, administrative proceedings, and case law development among the UK law, applicable EU cases, and US agencies and courts. It highlights potential improvements in the analysis of banking competition and the financial sector as whole. The ultimate goal of any proposed improvement should be to make banks and other financial institutions provide more efficient services and less costly products to consumers, while reducing systemic risk and preserving the soundness and safety of the financial system. The GFC led UK and US policy makers to introduce a number of laws and regulations aimed at addressing excessive bank risk taking and improving financial regulatory enforcement. The increasing interconnection between competition law and bank regulation means that the competition and banking regulators are well positioned to play an active and wide-ranging role. The actions taken by the UK, the US as well as other national and international bodies, upon the occurrence of the GFC, were arguably necessary and perfectly justifiable on regulatory and financial stability grounds. The GFC revealed a number of significant regulatory and central bank failures, and especially in terms of defective regulation, supervision, resolution, support and macro prudential oversight. A substantial amount of work has been undertaken to correct all of these. It is arguable that sufficient action has been taken to remove the worst threats that arise with 'too-big-to-fail'. This paper takes a comparative approach and examines the applicability of competition laws, policies, and methods in bank mergers in the UK and the US. It, also, discusses how to improve these laws, polices and methods to make them more efficient and better equipped to preserve and enhance competition in banking and financial system.