Tax Code Changed from 1196L to 535L - Why?

Hi, I currently have a private pension and receive a salary. My circumstances havent changed yet my tax code has changed this month from the standard tax code to a muc reduced one? Why?

Hi 

To confirm the reason for the reduction in your code, we would need to review your review your code for you.
To allow us to do this, contact us by webchat or phone via Income Tax: general enquiries 

Thank you