This may be very simple, but…..

we're travelling to the USA in April (Manchester-Las Vegas-New York-Manchester), which means we'll be taking 2 transatlantic flights with 2 domestic flights inbetween.

Both me and my partner plan on buying stuff, either in duty free or while we're in the US, but what's the score with carrying it? If we buy it on the outward flight from Manchester is there a chance it'll be taken from us by customs? Obviously we won't be removing the wrapping until we return home so they'll all be sealed. Am I reading too much into it and will everything be fine?

common sense FAIL

not sure about what NEW systems are in place since that tit tried to bomb the plane at christmas, but DF shops always were deemed to be inside the security system and therefore safe – they'd stand to lose a lot if that was changed, and generally money talks

thanks for that scaredypants. Maybe i'm not explaining myself (or maybe have no common sense), but my point was that once I got off the flight from Manchester I would be effectively leaving the "safe" zone and would then be trying to carry the liquids onto 3 more onward journeys.

I can't think what you would want to buy in customs going to the USA in liquid form that you either can't live without or can't get cheaper in the USA anyway.

IME, as long as you're staying 'airside' for all your connections there'll be no problem. On the way home, pack it in your suitcase…

I bought some body lotion at JFK duty-free and put it in my hand luggage as my case had been checked in. Flew to Heathrow terminal 5. Then transferred to Manchester. Body lotion was confiscated at Heathrow, and I caught my connection by 5 minutes due to the bastards taking about 30 minutes to check every tiny piece of my stuff.
If you buy make sure you put it in your suitcase and check it in.
Don't put any liquids in your hand luggage.

Buy in the US, pack into hold luggage for the journey back.

As long as you buy it airside you're fine to carry it on THAT LEG of the journey.

I do this loads.

Buy in Heathrow, carry on, no problems.

I pack it back into the hold baggage for the return leg (which is fine), no problems.

I don't tend to buy duty free in the US as, to be honest, it ain't good value. But you still can, as long as it's airside, OR, be clever and browse the duty free mag on the way out and buy on the aircraft.

And also don't forget most international terminals at Heathrow have landing duty free so you can shop once you've landed (but not with as much choice).

It's not a problem if you're sensible.