Firstly see if they can clear any block at BHD, it probably just needs a scan of your passport there. Then proceed as normal to Flight Connections Domestic after you arrive. If the HAL operator gets a "refer to airline" message then you can go to the Customer Service desk immediately to the left to do the visa check. If are early off the aircraft, and you suspect a number of people behind you will be going to the Customer Service desk (e.g. late flight) then you may want to go there first just in case a slow queue builds up while you go through the HAL scan line. But you only need to do this if BHD look mystified and invite you to sort out an undescribed problem in LHR.

All ESTAs must have a passport scan registered somewhere down the line, it's a requirement to check you physically have the same passport as your ESTA.