|Geoffrey Bell (Chairman)|
A London office opened in 1873, closed in 1916 during World War I and then re-opened again in 1923. In 1939 certain banking business of London Merchant Bank Ltd. (established in 1873) was acquired followed by the current business of Goschens & Cunliffe (established in 1814) in 1941. The London business became Guinness Mahon Holdings, which merged with Lewis & Peat Ltd in 1974, forming Guinness Peat.
The firm decided to enter the securities market buying White & Cheeseman, a stock jobber, in April 1984.
The Group ran into difficulties in the late 1980s and demerged into three parts: the Guinness Mahon investment banking business, Fenchurch Insurance and the off-shore investment activities. The offshore investment activities in Australia and New Zealand (then known as Guinness Peat Group) were bought by Brierley Investments Limited (a business controlled by Sir Ron Brierley) in 1990 and the Guinness Mahon investment banking business was acquired by Bank of Yokohama in 1991 and then sold on to Investec in 1998.
Meanwhile, Fenchurch Insurance merged with Lowndes Lambert in 1997 to create Lambert Fenchurch, then with Heath Group in 1999 to form Heath Lambert and then with Arthur J. Gallagher & Co. in 2011 to form Gallagher Heath.
From April 1986 to August 1994, Guinness & Mahon (Ireland) Ltd was a wholly owned subsidiary of Guinness Mahon & Co., London. The bank's Irish private banking operation was acquired by Irish Permanent on 31 August 1994, and operated from a single location. The operations acquired were scaled down in 2000. There were also companies associated with Guinness & Mahon (Ireland) Limited and Guinness, Mahon & Co., London, who placed deposits with Guinness & Mahon (Ireland) Limited. These companies were - Guinness, Mahon (Guernsey) Limited, College Trustees Limited, Guinness, Mahon Jersey Trust Limited, Overseas Nominees Limited and subsidiaries of Credit Suisse.
- Jonathan Guinness (November 28, 1998). "Was it pure genius?". The Spectator.
- "Guinness Mahon and Company". London Metropolitan Archives. Retrieved 14 November 2023.
- John Orbell/ Alison Turton: "British Banking - A Guide to Hosiorical Records", Ashgate Publishing, Aldershot 2001, p.243, ISBN 0-7546-0295-8
- O'Sullivan, Brian (2018). From Crisis to Crisis:The Transformation of Merchant Banking, 1914–1939. Springer International Publishing. p. 341. ISBN 978-3319966984.
- Guinness Mahon goes up for sale 21 January 1998
- Weiss exits Guinness Peat but stays on at Coats The Australian, 1 April 2011
- Investec enlarges its footprint Business Times, 1998
- About Gallagher Heath
- "IL&P trims Guinness & Mahon arm". www.independent.ie. 1 May 2000. Retrieved 12 April 2017.
- "Homepage". Office of the Comptroller and Auditor General.
- "Guinness Peat Group appoints four new directors". www.guide2.co.nz.
- "Guinness Flight Hambro - Investec merger finalised". November 13, 1998.
- Ivy Frances Jones (1974). The rise of a merchant bank.