I don't know if this is a known cloud formation or not, i do know that i've not seen anything like it before. It almost looks like a strand of DNA....
Shot high on Dartmoor..
After a google search it would appear these clouds are called;
Appearing as a slender, horizontal spiral of cloud, cirrus Kelvin-Helmholtz is one of the most distinctive cloud formations. However, it tends to dissipate only a minute or two after forming and, as a result, is rarely observed.