I have an upcoming trip to LHR, all booked through UA, with the return scheduled LHR-DUB on Aer Lingus and DUB-IAD on UA. I know UA has some arrangement with Aer Lingus but as I will not be departing LHR on a *Alliance flight will I be denied access at LHR? Any experience of this?

As far as I can tell I will have no access in DUB either as according to the UA site their arrangement with Aer Lingus is for business class access only to the lounge and that segment is in Economy. Again does anyone have experience that might suggest otherwise?