"The vast majority of R1b1a2 men who are deep clade tested fall within the two big supergroups P312+ and U106+ so it's quite unusual to find men who fall outside these big groups. I wonder if it might mean that your dad's ancient ancestors were amongst the original people who settled in Devon after the Ice Age. We will no doubt learn more as more research is published. Tibor Fehar, the admin of the R1b project might be able to tell you more.
Today I received an email from Tibor Fehar, an expert in DNA, with further interesting information: