Originally Posted by
SavvyTravel
But I’m trying to book two seats on a U.K. to Europe return using two vouchers. Both of us are in the same household account.
This is an old thread now, but I'd never use an upgrade voucher on a quick trip to Europe. It's an expensive voucher to justify on effectively short haul. Always keep them for the longest trips. For example, I booked a return trip in J to JFK for only 80000 Avios + voucher as it upgrades you from WTP to J, so it's very cost-effective both in Avios and tax payment.