Well, let's just look at the language of the main prayers in the Commons:
"Lord, the God of righteousness and truth... so may your kingdom come and your name be hallowed."
And in the Lords:
"O Lord our heavenly Father, high and mighty, King of kings, Lord of lords, the only Ruler of princes..." "Almighty God, by whom alone Kings reign, and Princes decree justice; and from whom alone cometh all counsel, wisdom, and understanding; we thine unworthy servants, here gathered together in thy Name,"
And of course the Lord's Prayer does heavily suggest there are no other gods...
But at any rate, if someone thinks it's billocks, why does it matter? Why does reciting a bit of fiction render the meat offensive?
I'd say that having prayers relating to one religion only, to the exclusion of others, in a parliament making laws that aply to everyone is a damn sight more problematic than reciting a bit of poetry near meat. But it's not really logically defensible to say that meat that has been prayed over is or should be unacceptable for those of other faiths or none, while a parliament that is prayed over is just peachy to those who don't follow the faith of those doing the praying.