I've done informal panel interviews (seated around a table, over lunch, etc.) but only in the US.
Think of it this way - they wouldn't have asked you in for an interview if they hadn't thought you were a good fit for the job - so be confident! And just be yourself - that sounds so cliche, but I find that if I can get it into my head that
I'm also checking
them out and just find the inner confidence that I'm worthy of the job, I interview pretty well....
With panel interviews in general, I think one really important thing is to address all of them - if one asks a question, make eye contact with each of them as you answer - keep them all feeling included.
Good luck - let us know how it goes! And congratulations!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!