Can I have a watermelon in hand luggage?

While I am unaware of any liquid list containing a watermelon, here's the biggest list of liquids I am aware of, from Debrecen airport:

All drinks (including beverages, water, soup, syrups), chocolate creams, creams, oil, cheese spread, liver cream, pastas, peanut butter, yogurts, cottage cheese, butter, margarine, frozen food, tins, liver wurst, sausage, jelly, mousse, hair colorants, mascara, fluid lipsticks, fluid masks, lotions, spray and roll-on deodorants, perfumes, nail polish removers, and all items made of similar substances.

Of course, there's nothing to guarantee the UK will use the same list but knowing how the UK is batshit crazy about airport security I bet their list is even worse. If liver wurst and sausage is a no-go then you can bet a watermelon won't pass either.

Watermelons can easily be loaded up with other liquids including potently explosive liquids and as such would likely be prohibited as carry on items. Perhaps folks in the UK would not be familiar with this aspect, but in parts of the USA the process of spiking watermelons with a bottle or two of whiskey is commonly done to get alcohol into venues like outdoor concerts, sporting events, where alcohol is otherwise banned.

But one has to ask, are the watermelons that good in the UK?

Sharing my personal experience on the flight from Venice to Gdansk with three legs and thus three security checks (Ryanair uses cheap small airports where you can't transfer) in Treviso (Italy), Beauvais (France) and Modlin (Poland). I have got a small watermelon (15cm in diameter) in my backpack, which I took as a cabin baggage. During baggage scans in Italy and France I was asked to open my backpack and security officers checked it manually. Once they found the big berry, they smiled, started joking with their colleagues and let me proceed. I was asked no questions and had no additional checks in Poland.

P.S. I like watermelons :)