<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by zurbec:
LHR-BCN is on separate itenarary from US ticket, so it is a bit more confusing.</font>
I would try to send the tickets to your friends in advance (or have the tickets changed to electronic form). IF your inbound flight is delayed or you get held up in transit and you miss your flight to BCN, everyone is up the creek
sans paddle. If they have the tickets and can go on, at least only you will be.
As for your proposed transfer from T4 to T1, it's as good as any. I am sure you can get out of the departure area at T1 by going through U.K. immigration but it may be a hassle in itself.