I find it quite hilarious when anybody over praises themselves, I think there are ways of doing it without being a complete big head recognising a strength or attribute but there are those who massively big themselves up, quite oblivious to how that might sound. I knew a mother down at the school gates, who was an aromatherapist, prone to saying something along these lines, "I have clients who beg, literally beg me to give them tips on clothes and make up because they are so envious of how I look" often to suppressed snorts of laughter from anyone in earshot as she boasted away without a flicker of embarrassment
Back to Mary Berry, I haven't seen her lately I do have one of her books, I suppose it could be a thing with tv chefs to stand back and admire their work, maybe we all do it to an extent. One of my sons sends me pics of some of his efforts with a "yes! before you say it, your son is amazing in the culinary department" said very much tongue in cheek.