Answer
Use regular expressions in order to capture the value of URL parameters. In Tableau this can be achieved with the built-in formula REGEXP_EXTRACT_NTH, for example:
REGEXP_EXTRACT_NTH ([URL], '(Category=)(.*?)&', 2)
This formula will capture the value of the "Media" URL parameter. To capture the value of other parameters please just replace the parameter in the formula, for example for "Media":
REGEXP_EXTRACT_NTH ([URL], '(Media=)(.*?)&', 2)
And the following formula will capture the value of the "Programme" URL parameter.
REGEXP_EXTRACT_NTH ([URL], '(Programme=)(.*?)&', 2)