If you're doing the 4 shirt multi-buy option, I'll point out that you're probably far better off buying from the UK site. The exchange rate is super low right now for GBP (~1.4) so 25 quid per shirt is significantly less than $50.
Factor in 14 quid for shipping (though it will be slightly less if you buy over the phone) vs. free shipping on the US site if you use a code, and you're still better off UK.
Once there's no free shipping option, use UKTIE50 to get the free tie.
Bottom line, 4 shirts for around $160 (instead of $200), and each additional shirt is $35 (instead of $50).