I thought this might be Sedum album or Sedum anglicum, the petals had a tiny hint of pink to them.
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I think this fits English Stonecrop as the petals can have a hint of pink. White Stonecrop has its flowers clustered on a long stalk.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Lat/Lng: 50, -5
OS grid ref: SW851154