Originally Posted by KARFA

You won't be able to do that if you don't have an onward bp. There is a HAL agent at a glass door between gates A23 & A22 (DUB gates) and the corridor continuing around to FCC. They will want to see a bp for any onward flights from LHR to let you pass.

Without an onward bp you will have to exit via the DUB arrivals corridor which comes out past passport control.