If you have a UA club membership, you can use the LHR UA club (which is great) with any same day ticket. Otherwise, no on Aer Lingus even if in F. There are a number of PP lounges in LHR (and DUB) you can purchase access to. You can also purchase access to the Aer Lingus lounges in LHR and DUB with loungebuddy. Subject to limitations, as usual.