Vulcan: They are definitely at fault & you are correct; the current rule of the Highway Code reads: “You should… never ride more than two abreast, and ride in single file on narrow or busy roads and when riding round bends”.
If they belong to a proper cycling club they may wear identifiable jerseys, if you can find out who they are you should make a complaint to the police, who could caution them.
And in relation to the OP it further states regarding designated paths;
"These paths can be used by pedestrians, cyclists, joggers and dog walkers. Nobody has the right of way, so all users are equally responsible for their actions. As a cyclist it's important that you keep your speed down and watch out for others."
Which seems to be sensible advice.