In theory yes. Now sure if you mean LGW or LHR. But separately from COVID, there is a longstanding requirement for a passport scan to USA. So what you can do is enter your passport into one of the self service check-in machines, using that not your PNR. It should find your reservation and do the scan in one step. If you get a paper or app boarding pass anyway, you can do it at the gate in LGW (but not LHR T5) but the BA lounge is a better location if you have access.