There are just two acceptable British occurrences - this current Oxfordshire bird and an immature at Sennen Cove and environs (West Cornwall) from 27 July 2008 until at least January 2009 (fully documented by Martin Elliott in Birding World 21: 462-466).
The species was initially added to the list on the basis of several records from Ireland, the first as long ago as September 1994. There are now at least six records -:
1994 Kerry Blackrock, adult, 17 September (Pete Morris) (published photograph in British Birds 90: 381)
1998 Mayo Newport Landfill, adult, 30-31 January (Pat Lonergan)
2004 Dublin Sandymount Strand, adult, 9 October (Niall Keogh), presumed same, 5 October 2005 (Niall Keogh), from 6 December 2006 to 10 January 2007 (Niall Keogh et al), 25 March (Niall Keogh) and 20 September to 5 October 2007 (Hugh Delaney, Niall Keogh, et al).
2005 Kerry Smerwick Harbour, adult, 24 July (Paul Moore)
2006 Kerry Carrahane Sands, adult, 6 September to 15 October (Tom Lowe, Keith Langdon, Tom Lowe, et al) (Birding World 19: 391-392)
2009 Cork Castletownbere, 3rd-winter, 23-25 January (Dave McAdams et al)
I am indebted to Niall Keogh for information from Ireland and to Mark Golley for additional information on the British occurrence.