As others pointed out, you might get away with it as is – it depends. Without seeing the scratch/damage, it’s hard to make a prediction.
Despite what Wigwam says, scratches can and will impact your GCB depending on severity. If the scratch is down to the metal, as a rule of thumb, it needs doing. This is an actual measure from their “end of lease” inspection, they categorize scratches into three categories, and can be seen here.
Of course if the tail light is actually broken and not just scratched, it needs doing anyway for legal reasons – it’s not quite obvious from the way you phrased it. If the function is impacted, you risk being fined if police notices it, and it’ll fail MOT.
As kezo said, if you supply us with a picture, we could make a more accurate description.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.