(Baggage) interlining/transit formalities between BA and AI at LHR

Question

In a few days, I will be travelling from Bangalore, India to Berlin, Germany via New Delhi and London, i.e.:

BLR-(AI173)->DEL-(AI161)->LHR-(BA992)->TXL

The entire journey is booked on one PNR and ticket.

As per the Air India website, the Indian customs and immigration formalities will be handled in BLR so that in Delhi, I will technically be performing an international transit.

My question, however, relates to the transit in LHR. Will Air India be able to check my baggage through all the way to TXL? Additionally, will Air India be able to issue a boarding pass for the last (BA) segment of my journey?

Possibly related: In my understanding, the transfer in LHR should again be international, i.e., no customs or immigration. According to the LHR connection planner, this understanding seems to be generally correct (no mentioning of passing through immigration) even though I will arrive at Terminal 2, while my onward flight to TXL leaves from Terminal 5. It does however say

You will pass through security screening at this point. If you are a non-UK resident and have goods to declare to HM Customs, please use the Customs telephone before security control.

Why would I need to declare anything to UK Customs when I'm not even (technically) entering the country?

Answer 1

Will Air India be able to check my baggage through all the way to TXL?

Yes, your bag will be checked through to your BA flight for delivery in TXL.

Additionally, will Air India be able to issue a boarding pass for the last (BA) segment of my journey?

Maybe yes, maybe no. Depends on many factors, from the quality of their IT implementation to whether BA operations has locked the flight for editing when you check in in BLR. When you get to Terminal 5, there are desks before security, on your right, where you can get your onward boarding pass printed, if necessary. The signage is clear. You won't be able to proceed to security without your boarding pass, so you cannot miss the desks. You may also be able to obtain your boarding pass on the BA App.

In my understanding, the transfer in LHR should again be international, i.e., no customs or immigration.

Correct. (There is a security screening for all internationally originating connecting passengers.)

Why would I need to declare anything to UK Customs when I'm not even (technically) entering the country?

It is probably a miscommunication. Formally, passengers connecting to UK domestic flights may need to make a customs declaration at Heathrow if they are carrying on their person (not in checked luggage) items that require declaration.

Answer 2

tl;dr: Calchas was completely right, but I had to fight a little

So this is what happened: When I arrived to BLR airport, the lady at the check-in counter told me I would have to pick up my luggage at LHR, go through Customs and re-check it. When I asked her why she wouldn't check it through all the way to TXL, she said something along the lines of "we don't have a codeshare agreement with British Airways" (which is true, but irrelevant) and "LHR is your first port of entry", which doesn't make any sense.

So I pressed her a bit about what she believed I was going to enter exactly, and asked her directly to consult her supervisor about the issue. She was clearly reluctant to do so, but in the end she asked the colleague next to her, who told her to check it through to TXL.

In LHR, I showed my luggage tag to the BA transfer counter just to make sure and they confirmed that my luggage had made it to the transfer process and indeed, I could pick up the luggage in TXL without any problems.