Join Date: Jan 2011
Location: usually somewhere between 30000 and 40000 feet...but actually the English countryside
Programs: BA GGL/Lifetime Gold, EK Gold, Lowly M&M, Marriott tit, Hhonors Diamond, numerous others
Posts: 1,156
Welcome to FT.
You will only be offered 1 upgrade (if at all as the pay upgrades may have all gone) so eg WT to WT+.
General rule most people work to is to select the class of booking you want to travel in at the time of booking. If something comes along either as a paid or free upgrade then that's a nice bonus.
Have a good trip whatever cabin you are in and enjoy Blighty.
By the way, the surly immigration folks are not your typical Brit!