I am travelling from Newcastle (UK) to India and I am assuming I will get all my boarding passes in Newcastle check-in. However, I have a layover in Heathrow and I had this doubt that if I have a boarding pass can I go through the security in the departure level? The layover is for 12 hours, it won't be that long till the time I reach the terminal 4 from 5.
Your Newcastle to Heathrow flight is an internal UK one, and when you arrive you can leave the airport and return in time for the next flight. It does not matter whether you have your boarding pass yet or not, as you do not need it to leave the airport, nor on your return to get into the buildings. You need it before you get through security on the way in.
Make sure you leave enough time for the travel, security and if you do not yet have your boarding pass for getting one. For in international travel 3 hours is usually advised, but if you need to take several (underground) trains, leave a little more time as each connection may lead to a missed connection.
You cannot clear security before you have your boarding pass for your onward flight.
- You will receive the boarding pass for your flight from Heathrow already in Newcastle
- After you land in Heathrow, you go to the transfer desk and get your next boarding pass there
- You leave the secure area before you have the boarding pass for your onward travel. In this case, you will need to go to the check-in area of the terminal from which you are departing and obtain it there.
Either way, 12 hours of layover time is enough for all of these options. Option 3, I think, is not how it is supposed to be, but if you happen to leave the secured area without having to, it's the only option.