Derrick trained with Pannell Kerr Forster, qualifying in 1972, and joined Frazer Whiting & Co (a predecessor firm of Littlejohn) in 1973 as an audit manager. He became a partner in 1984.

Derrick acts primarily for smaller to medium sized owner managed enterprises and corporate entities in a financial advisory capacity. His specialisms include raising finance with banks and other financial institutions, and in over 30 years he has developed many contacts in the banking sector. He also specialises in advising on buying and selling businesses and all matters relating to running a family business.