A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
DL and VS have a close partnership, so it should be easy to find a connection using DL and VS from SEA to LHR. OP should research this, decide on the preferred route (tell the phone agent flight numbers, times, and dates) and then ask VS to change the ticket (for free), assuming that travel close to the original dates is still desired.