Duplicate /blog/ in category URL's

Hi,

I am getting duplicate /blog/ ‘bits’ in my URL’s for categories. This does not happen for tags or archives. For example

Main Site: https://www.jonrouston.co.uk/blog/
Category example:https://www.jonrouston.co.uk/blog/category/blog/wedding/
Archive example: https://www.jonrouston.co.uk/blog/2010/11/
Tag Example: https://www.jonrouston.co.uk/blog/tag/derbyshire/

Anyone know how I can remove the duplicate /blog/ ?

I’m using atahualpa

Thanks
Jon