Stig mostly capable racing around though it's not good for the environment (7,3)
I believe the answer is:
plastic bag
'it's not good for the environment' is the definition.
(plastic bags are bad for the environment)
'stig mostly capable racing around' is the wordplay.
'mostly' means to remove the last letter.
'racing around' indicates anagramming the letters.
'capable' with its last letter taken away is 'capabl'.
'stig'+'capabl'='stigcapabl'
'stigcapabl' anagrammed gives 'PLASTIC BAG'.
'though' acts as a link.
(Other definitions for plastic bag that I've seen before include "Shopping carrier?" , "Supermarket shopper" .)