I saw the programme. Whittingstall didn't highlight a ridiculous quota system as far as I can see, he was blaming it in order to try to absolve the real culprits. The scandalous waste of fish was clearly indicated to be down to appalling (maybe deliberately so ?) management of the catch by the boats. If they deliberately fish to the limit, knowing full well they'll catch more when fishing for other species, and heartlessly not care but sling dead fish back in order to stay legal, then there is only the catch management to blame. If they fished to within the limit before swtching species, problem solved.
As for mackerel, one of my favourites. Yes I buy tins, but of course the best way to have fish is fresh and done well. One despairs at a human race that simply has no ability to control itself and avoid these sorts of issues.