Aeonium arboreum 'Schwarzkop' a native of the Canary Isles... Is frost tender so needs to be in a cool greenhouse for most of the year.

Take a look at he RHS info:

https://www.rhs.org.uk/Plants/83034/Dark-purple-houseleek-tree/Details

Has been seen occasionally on the SRGC show benches but not accepted as is no hardy.

Agree Aeonium Zwartkop or Black Rose Sedum

If you bring it indoors for the winter, without sunlight, it turns plain green, so a sunny windowsill would be good.

Thanks for your help.I have had it on the top of my water butt all Summer & it has produced lots of rosettes in that time. 

Won't survive the winter outdoors though... as Bamboo says will need a sunny windowsill and keep moist.

Its easy to propagate new plants from the rosettes. Each rosette can be a separate plant.