How long to get through customs at LHR?

I go through LHR about twice a year. In the past few years it seems to have gotten a little faster or maybe I have just gotten use to it. Your 2:10 should be okay if your flight is relatively on time. LHR actually has a pretty good website that does have some times between terminals, and recomendatins. http://www.heathrowairport.com/heathrow-airport-guide

It's immigration (passport control) that you have to worry about, not customs. Looks like British Airways recommends connection time of 60 minutes.
ttp://www.heathrowairport.com/heathrow-airport-guide/flight-connections/terminal-5-international-connecting-to-terminal-1-republic-of-ireland Their guide probably assumes both your flights are on the same ticket though.

If you have bags to check, BA might not through check them on separate tickets, especially since one is a code share (do check as policies change). If they won't you will have to collect them, go through customs, and do the terminal connection landside. This is free via the Heathrow Connect or underground, although the latter would require an Oyster card to get through the barriers. With the Express running at a 15 minute interval your journey time could be up to half an hour if you are unlucky. Then you would need to recheck with Are Lingus in T1 and go through security. It is doable but tight, and not resilient against any delay. If you can connect airside it would be easier, but you would still be on your own, or at the mercy of Aer Lingus if you didn't make it before they close.

Hello Dave. I flew to and from London's Heathrow airport, more than once. I recommend : change to a later flight time for your flight from LHR to Dublin.

Time isn't so much a factor as luggage is. Staying airside, two hours 10 minutes is plenty of time to make the terminal shuffle. I've done the "terminal shuffle" to/from Terminal 5 numerous times, and can typically go gate-to-gate in an hour. The problem is going to be collecting bags. If you do this with all hand luggage, you're golden. I don't know BA's policy regarding cross-checking bags, or if you can collect your bags airside for your Ireland flight. For that, you'd need to check with them. If you can pack light enough (carry-on), you are fine the way you are. If you have to clear immigration to get your bags, shuffle terminals land-side, and re-enter security in Terminal 5, you are better off going for the later flight.

People are saying customs when they mean immigration/passport control. That is what takes time. If you have to collect and re-check bags, you have to go through immigration as technically you are entering the UK then. That line can take an hour or more, depending how many other planes arrive. If your bags are checked through, or if you have carry-on only, you can transfer between terminals airside without going through passport control. This is much faster. But somehow I thought there were special rules for Terminal 1 and flights to Ireland, like maybe you have to go through immigration and cannot transfer airside. Am I imagining things, or does someone know what I am thinking of? If there is no special or different rule for T1 departures, and you have carry-on bags so you can transfer airside, you have enough time IF your US flight arriveson time. That part is still a gamble.

According to the Heathrow Flight Connections instructions, if you are arriving T5 on an international flight and going to T1 for a flight to the Republic of Ireland, you can connect airside on a dedicated bus, but you still go through passport control and biometric screening at T1. It must be faster than passport control at T5, as it says the minimum connect time is 60 minutes. Mthat is without transferring luggage, however. As pointed out above, if you have checked luggage and need to pick up and re-check it, that will take a lot more time.

Hey thanks all of you for your great input. I should have said that we do intend to pack light and carry on-and arrive early for flight to London. I'll speak to BA about staying airside and confirm, but I think we'll just go for it and hope for the best. Thank you again, I appreciate it!
Dave

The UK and Republic of Ireland operate a 'Common Travel Area' which means that you have to clear immigration at the first point of entry. However, customs formalities, such that they are for most travellers these days would be prior to leaving any airport enroute. The RoI does operate a passport check on entry from the the UK at Dublin Airport - but there is no passport check arriving at any UK airport from the RoI. The 60 minutes quoted above is the minimum connection time allowed when travelling on a single ticket. Aer Lingus requires check-in 45 mins before departure, but you may be able to manage that electronically - but this must be no less than 2 hours before departure.

Like several other replies we go through LHR several times per year. The time varies and customs is not the problem. Immigration is the problem. Although LHR is far more efficient than any of the US ports of entry the shear volume at H.R can lead to long lines hence long waits. We always allow 0 mins for this this process knowing full well that it may go fast and then have lots of extra spare time. The transfer to Term 1 can also take time depending?
Best advice check with B.A. try and get some one who has actually done the transfer rather than one in a cubicle looking at a chart thus parroting the official policy which only takes in to account the average time needed with no glitches. Good luck and enjoy your trip. LHF

From LHF: I meant 90 mins not Zero.
Sorry. LHF

Thank you all again-I spoke with British Air and they confirm that there is a BA shuttle to get us to Terminal 1, and that if it turned out we had to check baggage they would "check it through" to the Dublin flight. Fingers crossed.
Dave