Upvote:0
If it's in a single booking, you usually have little to lose by booking that trip, because if you miss the connection, you'll be put on the next flight for free. You also don't clear immigration, but will clear security
If it's on separate tickets, you will need to clear immigration there's no way 1 hour will be enough.
Upvote:8
You won't have to go through passport control since you are not entering the UK (assuming you have booked this as a single ticket), but will have to go through security screening.
You can use the Heathrow Connections tool to see exactly what you'll have to do and how long the airport wants you to allow. Just enter the flight numbers.