CPI costs can be transferred to customers?

I was having a discussion with a colleague about our company passing on inflation costs as CPI costs onto the customers today and it got me thinking. Currently we also add an additional premium on top of whatever the CPI was in january, so lets say the CPI was 4%, we add an additional 4% making it 8% ( so not an additional 4% after having added 4% cpi) and pass these costs onto our customers every year, once a year. However we were wondering if the terms of the T&C's that state we are passong these costs on due to inflation are correct or if it falls into a different category entirely. This is a question simply as a thought process only, my colleague and i are in no position to actually make changes at our company, we are just wondering if it should fall into a different category becausethe second 4% is an arbitrary number and not directly related to actual costs or inflation figures in any way.

Hi mrssomerset MRSSO,
Unfortunately we cannot answer hypothetical questions nor provide accountancy advice.
You may need to seek the assistance of a professional tax advisor/accountant. 
Thank you.