At last, after years of trying, successful carrots. Usually they get attacked by carrot root fly that can supposedly smell a carrot from half a mile away and burrow beneath the soil into the carrot to lay their eggs. They don't fly very high above ground level, so having raised beds can help, as can horticultural fleece. Another remedy is to confuse the little blighters by putting mint and lavender between the rows - especially after you've pulled a few carrots up and disturbed the soil - and it's best to harvest or thin them on a windy or wet day, when they'll probably not be flying. Even if the fly doesn't get them, the badgers might.