What time do you make it?

I took the photo of the sundial at 14.40 BST. The shadow was on exactly 13.00. I can cope with the fact that it said 13.00 instead of 14.00 because of British Summer Time but what has happened to the extra forty minutes? My companion thought it was something to do with latitude but I am inclined to think that the sundial was incorrectly positioned!
This magnificent sundial (even though it tells the wrong time!) is near the rose garden at Polesden Lacey. On this beautiful day the gardens were busy with visitors. The spring bulbs have finished and there were few roses out yet but there was still plenty to see. It is always interesting identifying plants in the huge herbacious borders. Polesden Lacey is a National Trust property, so of course there was tea and cake at the end of the walk.