These are the sort of cyclist I find really annoying.
Just because a group of people are out with their club on a run doesn't mean that the laws and rules of the road don't count. They are no more 'one vehicle then, say, a funeral convoy or a group of mates out in their cars would be.
Shouting out 'stopping' is a bit daft too as each person should be prepared to stop and leave a sufficient gap to stop safely. Bike generally don't have brake lights and indicators but the riders do have arm signals they can use.
Last year I was driving along a narrow single carriageway with only a single lane each way. The road was national speed limit. Coming towards me were a group of cyclists in a pack riding fast and three abreast. I slowed from 60 to 50mph and moved over a little to reduce wind draft.
As we got closer it suddently became four abreast and then just before we passed it became 5 abreast with the fifth one frantically trying to pass the others and on the wrong side coming at me causing me to have to brake hard and swerve off the edge of the tarmac to avoid him.
Nothing against them going for a fun ride or a 'race' but attemting suicide with my car is another matter.