The leader of a walk has the absolute right to choose whether dogs are permitted on walks.
Some groups do not permit dogs on any walks. Some groups positively welcome them.
Please respect these conditions.

It is appropriate to call the leader before the walk to check if dogs are acceptable.

Many walks are not suited to dogs whether because of livestock or other conditions, but in general, leaders are often happy to permit well controlled dogs.

You are expected to have full control of your dog at all times.
If in doubt about letting your dog off the lead please ask the leader.

Long leads are dangerous in group walks.
Please either use a short lead or be certain you dog behaves suitably in groups.