For solo travelers
Advice and tips for single travelers in the U.K.
Some single penalties are implicit.
A single room at a hotel rarely costs exactly half of what a double one does (it's usually more like 70%–80%).
When two or three of you rent a car—even if only one person drives it—you still split that cost evenly.
Then there are all the little extras.
There's no one to share the cost of the meal (perhaps you would have shared that secondo, and a bottle of wine).
It's sometimes tough to book a day trip, as they often have a minimum participant requirement before they'll go (though you can glom on to a trip that already has participants).
There are often menu items (risotto in particular) that require you order for a minimum of two.
The good things about traveling solo
That said, I spend the vast majority of my travel time going solo (part of the job, you see), and while it might cost a wee bit more, it's still extraordinarily fulfilling.
I get to do what I want, when I want. No negotiating over when to get up, what activity to do or sights to see, where to eat out, and where to head next. I am master of my own itinerary and my own daily schedule.
I tend to notice and absorb a whole lot more of my trip, since all of my attention is focused outward, on the destination, not split between what I am seeing and paying attention to the person or people I am with.