[NOTE: THIS IS NOT EXHAUSTIVE. PLEASE FEEL FREE TO POST ANY ADDITIONS OR CHANGES IN THE COMMENTS BELOW.]
Conservatives: The “Countryside Communities” section of the 2017 manifesto was silent on the issue. Theresa Villiers has recently pledged to protect the freedom of Jews and Muslims to practise halal and kosher slaughter.
Labour: “Mandatory labelling of domestic and imported meat, including country of origin, method of production and slaughter (stun or non-stun)”
Lib Dems: Page 14 of this 2003 policy paper suggests the party supports religious non-stun slaughter.
Plaid Cymru: no policy as far as I can tell
UKIP: Previously said “Legislate for food labelling to show country of origin, method of production, transport and slaughter.” Now calls for ban on domestic non-stun slaughter but allows imports subject to clear labelling.
Ulster Unionist Party: “We want to respect all religious beliefs and practices. However, we also believe animals should be slaughtered under the most humane conditions possible. Evidence clearly indicates that slaughter without pre-stunning can cause unnecessary suffering. [Spoiler: actually it doesn’t.] As such, we believe animals should be stunned before slaughter. In the meantime, we believe that all meat products should be labelled clearly to include the method of slaughter.” (p. 6)
Sinn Fein: no policy as far as I can tell
Alliance Party of Northern Ireland: none as far as I can tell
English Democrats: no policy as far as I can tell
The Brexit Party: no policy (obviously!)
ChangeUK: no policy as far as I can tell
The Renew Party: no policy as far as I can tell
Time Party UK: labelling
Democrats and Veterans: no policy as far as I can tell
The Official Monster Raving Loony Party: none (disappointingly)
Foundation Party: scroll down for their “Agriculture and Fishing” platform, which says, “Ban the export of live animals for slaughter and require that the presumption should be that animals are stunned before slaughter. Exceptions to this should require the highest animal welfare standards to be observed… Legislate to ensure that animal products are labelled to show the country of origin (not just packaging), method of production and transport and whether the animal was stunned before slaughter plus information concerning hormones and GM products”
Liberal Party: no specific policy
Libertarian Party UK: none
BNP: support a ban on religious slaughter but not on fox-hunting, which (one might think) suggests they are not entirely motivated by animal welfare
Britain First: ditto
SDP: used to call for an outright ban. Now says this:
The quantity of meat slaughtered under the Religious Exemption shall not exceed UK domestic demand.
Export of meat killed by non-slaughter methods is to be banned and the Import of non-stun slaughter meat will also be banned unless the country of origin has equivalent animal welfare standards to the UK.
All meat product sold in the UK shall include clear labelling regarding the method of slaughter. Labelling to be clear if the meat is Halal or Kosher.