I found that the UK adapters weren’t working in most of the outlets in my hotel room in Belfast. I tried unplugging a hotel appliance and using that outlet. My adapter worked fine in that outlet!
Lesson: Hotel outlets get lots of use and may become loose. Look for an outlet that gets less use and try an adapter in that outlet.
I've run into loose outlets here in the US, too.
The UK has an added issue in that outlets have on/off switches. I assume that was not the problem?
Switches: Also note that what's "on" to my brain, is actually "off".
Yeah, I was going to mention the switches. If you were not getting any current, then the outlet was probably off. Items the hotel leaves plugged in (a lamp, a kettle) they likely leave the switch on.
Another reason to use a travel adaptor with multiple ports for your tech - Not all hotel outlets work, or many older hotels have limited numbers of outlets.
Regardless of however many adaptors/devices you bring, make sure the socket is switched on; otherwise, all will be in vain.
We each have a 1,5m N.American extension cord with triple-tap female. We secure the appropriate single european male adapter to the male end with tape. This allows us to access power outlets behind furniture but keep our devices and chargers at hand and within sight (in the interest of both convenience and not forgetfully leaving them behind).
As for using loose public or airplane outlets we keep a dab of bluetac (think of chewing gum that pulls off cleanly) wrapped in cello in our RS tech pouches.