Permalink Issues with /%postname%/

Hey Guys – I am struggling to get the correct URL “pretty link” structure.

The issue is as follows. I have set /%postname%/ as the structure and it works fine except for categories, where it inserts an additional word before the /%postname%/

i.e. http://www.airport-parking-quote.co.uk/reviews/airport/edinburgh-airport-parking-reviews/ (where does the /airport/ come from?)

Once you click through to the individual posts, the structure works fine.

Any help would be greatly appreciated!