The common megrim Lepidorhombus whiffiagonis is a commercially important, high-value flatfish species. From the early 2000s, discarding of common megrim in the northern North Sea has been widespread. In this study, we investigated temporal variation in megrim discarding in the mixed demersal fishery in the northern North Sea before, and following recent quota increases. Furthermore, logistic regression models were applied to investigate the effects of a range of explanatory factors on the probability of individual fish being discarded. Results indicate that discarding on the vessels sampled has declined from an average of 54% of the total common megrim catch in 2009 to 20% in 2012. The decrease in total discards was primarily a result of a decrease in the proportions of discards categorized by the crew as small within the catches from 0.39 (±0.02 s.e.) in 2009 to 0.10 (±0.01 s.e.) in 2012. Model outputs also suggest that the likelihood of a fish being discarded decreases significantly (p < 0.001) with increasing quota. The current megrim total allowable catch serves only to regulate landings and does little to regulate fishing mortality. Additionally, the proposed reform of the CFP, including the move towards a discards ban and the implementation of maximum sustainable yield, raises a number of concerns that need to be addressed if the northern North Sea mixed demersal fishery is to be managed sustainably and remain economically viable in the future.