If someone is keeping a secret, in the US one might say "tell me!" However, I was in the UK and I heard a person say "tell us!" although she did not appear to be with anyone. Am I misunderstanding or is this common?
Yes, it's quite common. It's non standard British English, akin to the "royal "we"".
I use it sometimes myself, though I don't really know why. A couple of examples for you that I can hear myself saying:
When making my way through a crowd of people. (It's just me, though sometimes the "us" form sounds a bit nicer.)
Do us a favour!
Used in indignation similar to "Oh, please(!)". Your example is also one where this is a common trait.
This usage is even more common in Newcastle than the rest of the UK, often making its way into lots of everyday phrases.
Give us a call
Just me. Nobody else.
"Us" for me is common in the north east (of England) particularly Co Durham Land of Prince Bishops.
It's just an old English way of speaking. Many people say "us" but if they are writing will use the word "me". I was born in Sunderland and I use it some times, depends who I am talking to.
If you listen carefully you may notice
- "us" meaning me sounds a bit like "uzzz" and
- "us" meaning you and me sounds like "uss".
That's my family and friends anyway or anyhow as we sometimes say too!:).
Alan Bleasdale's emotive series "Boys from the black stuff" (1982) follows the unfortunate Jimmy (Yosser) Hughes as his life spirals downwards after he loses his job, working with a tarmac gang in Liverpool, to losing his wife and falling foul of the local authorities. Towards the end of the series Yosser, driven to despair, is seen begging for work with his much used request: "Gi's a job" a phrase meaning "Give us (me) a job." Actor Bernard Hughes' use of the vernacular expression added so much to the atmosphere of the scene, of a man desperately hanging on to his dignity in a hopeless situation.
"Us" meaning me appeared in Northern English dialect, (now almost lost in time)"Tha'll tellus owt" (You will tell me anything) as a riposte to an outlandish statement or excuse, tone of voice adding to the weight of the phrase. Here the 'us' often had a two-fold function interpreted as "you will tell me, and any other person in the room, anything, thus both singular and plural in one labour saving sentence, allying the speaker with others about him.