I am flying Phoenix USA to Stockholm Sweden via Heathrow/LHR. I'll have ~4 hour layover (connecting flights both Finnair). My carry on will be a package I want to mail to Germany (2 vintage framed pictures). Is it feasible/possible to do this at LHR? How easy/difficult to do?
If you have a 4 hour layover, you may need to pass through immigration and leave the terminal but that’s easily doable in 4 hours.
Here are the Post Office details at Heathrow:
The airport Post Office is on the first floor of Terminal 3 departures, in the public area before security ( it's near the security control entrance).
Opening hours: Monday to Saturday 09:00 - 17:30, Sunday 09:00 - 13:00. Telephone: +44 (0)20 8897 3463
Finnair flights leave from Terminal 3 anyway:
Finnair flights from Heathrow Airport will leave from Terminal 3, Zone G.
Considering it is the same terminal you should have plenty of time. All you need to do is exit the airport through immigration. The report from July states an average of 45 minutes for NON EAA Immigration, say it takes an hour to get to the post office, you will still have at least 2 and a half hours in the case of delays before your flight.