UA/CO send a link to your email which you open on your mobile phone's browser. I open and save the page so I can load it more quickly when I approach security/gate. I've used them all over the US, but not in Europe. Going to have to try it for my intra-Europe LH flights next month at ZRH and FRA!

EDIT: OP, Aer Lingus says that they have mobile check-in (and assuming BP) on certain routes out of DUB. BA says all flights out of UK except LCY-JFK.