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The colours do match those in the photo at http://www.rhs.org.uk/Gardens/Hyde-Hall/About-HydeHall/Plant-of-the-mont... and the specimen I saw certainly had a lax habit in that the main stem was resting on the ground for most of its length!
Euphorbia myrsinites has a lax habit.
But the leaves are a different shape.
Lat/Lng: 52.62706, 1.29676
OS grid ref: TG232083