Put the flags out!

Put the flags out!

An expression of extreme and pleasant surprise that something has occurred. Used humorously. Primarily heard in UK. Well, put the flags out—all our kids are up before noon!
See also: flag, put
Farlex Dictionary of Idioms.

put the flags out

or

put out the flags

BRITISH
1. If you put the flags out or put out the flags, you celebrate something special that has happened. Even now, they must be putting the flags out in holiday resorts like Bognor and Blackpool. Birthdays and christenings, or just a spell of good weather, are all the excuse you need to put out the flags and celebrate summer in the garden.
2. People say Put the flags out! to show that they are surprised but pleased that something has happened. The builders have finished? Put the flags out!
See also: flag, out, put
Collins COBUILD Idioms Dictionary, 3rd ed.

put the flags (or flag) out

celebrate publicly.
See also: flag, out, put
Farlex Partner Idioms Dictionary
See also:
  • corporation pop
  • council
  • council pop
  • as you do
  • and I don't play one on TV
  • "I see," said the blind man
  • there must be something in the water
  • are we having fun yet
  • Are we having fun yet?
  • believe it or not