Onside Accounting

Who we are

Onside are Chartered Accountants and Business Advisers supporting businesses in the UK across the services industry. We have a particular passion for supporting high-growth businesses.

The company was founded by Martin Brennan, a fellow of the Association of Chartered Certified Accountants (FCCA). Since qualification Martin has spent much of his career working in operational leadership and technical roles in high-growth accounting practices. Martin takes great pride in delivering high standards of work at all times and particularly enjoys developing people, with an excellent track record of converting aspiring young professionals into qualified accountants.

Our Vision

Onside's vision is simple. We want to be part of your story and we want you to be part of ours. We want our team and our clients to value what we do and more importantly, we want to enjoy it.

Our vision is reflected in our four key values:


Our business is fast-moving and adaptable to change


Our team can work flexibly, around your needs and ours


We are here to work together to support your business


We like to know the people we work with and enjoy it!

Our Services

Onside offer a vast range of accountancy, tax and other advisory services  - 

Accounting & Tax

Keeping on top of your filing responsibilities with HMRC and Companies House.
Learn More

Outsourced Finance

Outsource your finance department to us, enabling you to focus on your business.
Learn More

R&D Tax Credits

Manage your R&D tax credits application with the help of our expert advisors.
Learn More
Onside Accounting is a trading name of Onside Accounting Limited which is registered in England & Wales under Company Registration No. 13428300