This looks very much like our native Arum maculatum
, the Cuckoo Pint, I've assumed it has to be the same species - although I've never seen a yellow one before. (I'll try to find out more if I have time)
It's a pity this has been caught by a late frost which has made part of the "flower" turn brown.
Picture taken at Exbury Gardens, 29th March 2009.
**midday 2nd April ** update
Many thanks to the Head Gardener at Exbury.
This is Lysichiton americanum
, the American Skunk Cabbage (USA name = Western Skunk Cabbage).
It is a member of the Arum family - Araceae.
The plant is considered an "invasive alien plant by EPPO and is included on the EPPO Action List" because in some parts of Europe it has caused local extinction of native species. The situation is being monitored.
More information - here - .