Sedum kamtschaticum, probably. Could be Sedum hybridum which is very similar or Sedum Weihenstephaner Gold which is a form of S. kamtschaticum.

Thanks Owdbuggy, it has taken on very well considering I have just planted it in very dry hot conditions so a Sedum seems very likely.

Well if it grows like the ones in my garden it will spread. We even have one on the tiled roof where there is no soil at all.