Musk Thistle or Nodding Thistle (Carduus nutans)

Actually this is a WHITE one.

The normal appearance of the Musk Thistle or Nodding Thistle (Carduus nutans) is a shade of magenta. It is locally common on calcareous soils as here on the South Downs near Brighton. Occasionally, a pure white specimen is encountered.

Whatever the colour, the bees don't seem to mind.

A more normal specimen can be seen here:-