The EU's 2009 Slaughter Regulation requires all animals, including poultry, to be stunned before slaughter. Stunning is defined as any intentionally induced process which causes loss of consciousness and sensibility without pain, including any process resulting in instant death.
The UK has invoked the "religious exemption" from the EU's "slaughter directive" and in practice now carries out more halal slaughter than the rest of Europe. Traditional halal meat is expected to be killed by hand and must be blessed by the slaughterman. The exception allows for animals to be slaughtered without being stunned first.