Last year I saw the last bird on my ringing site near Aberystwyth on March 21st, on Thursday night (April 11th) I went to have a look and there were still 20 woodcock there! I caught 6, 5 were juveniles and 1 an adult. Three had weights which were below average, and the other three were pretty fat.
There can be little doubt that the cold weather and endless easterlies are the reason for this late departure, but now that conditions have improved we should be seeing them move off.
There is plenty of evidence from the continent that woodcock are on the move. Here is a chart showing sightings on the excellent www.waarnemning.nl website, it shows a large peak in woodcock seen on April 9th.