What i have found with a few club cyclists, there are a few who are not fast enough to go with the A group and seem to want to show how fast they are.
Feel sorry for them to some extent but the best way to deal with them is to just say steady when they pick the pace up.
There have been many times when i have joined in for a slow or steady cycle just wanting to use it as a recovery cycle and found myself in what seems to be a race?
My view is if some one wants to go faster than the group but still join in then theres nothing wrong with them getting at the back, stopping for 1 minute then trying to catch up, stopping again but for 2 minutes and again trying to catch up etc, i have invited a few to do this and always find that after the 4th catch up any want a bee racers have had enough and seem quite happy to sit in?