The Small Business, Enterprise and Employment Act 2015 introduced a new role to all United Kingdom companies, limited liability partnerships, CIC's and SE companies, called 'persons with significant control'. This study looks at all companies registered in the United Kingdom where another company has control where control is defined as: Ownership of shares - more than 50% Ownership of voting rights - more than 50% Right to surplus assets - more than 50% Has significant influence or control Right to appoint and remove members or persons This study examines only those companies that are controlled by other companies in the United Kingdom. There are 233,656 companies that are controlled in this way and there are 107,737 controlling companies. A companion study, Who Owns Whom: Foreign Ownership in the United Kingdom [ISBN 978-1-912736-04-1] looks at all companies in the United Kingdom controlled by foreign companies. The City Code on Takeovers and Mergers is a set of rules that apply to companies listed on the stock exchange. It is administered by The Panel on Takeovers and Mergers. Prior to 2006, the rules were voluntary but they are now statutory. In June 2018, the government made changes to the UK's merger regime to recognise the growing importance of small British businesses in developing cutting edge technology products with national security applications. The government amended the threshold tests for businesses in the military, dual-use, computing hardware and quantum technology sectors that are likely to have security implications. Ministers can intervene when the target business's UK turnover is more than £1 million, (down from £70 million under the previous rules) Recent acquisions: Zoopla Property Group PLC acquired Dot Zinc Ltd John Wood Group PlC acquired Amec Foster Wheeler PLC Busy Bees Nurseries acquired Treetops Nurseries The British United Provident Association acquired Oasis Dental Care Drax Group PLC acquired Opus Energy Group Ltd