I am travelling in Europe for work. The policy is economy but I would like to upgrade the outbound using Avios (the inbound has no availability.) I will have checked luggage for this trip. To avoid raising any eyebrows, I'd like to book a cash economy ticket and get a receipt and then UuA separately. I would prefer to have the lowest headline price on this receipt.

If I make a dummy booking via the "Book and upgrade" option this gives me Economy Plus for both flights for a total of £207, plus 10500 avios plus £17 extra taxes for the outbound upgrade.

If I make a dummy cash booking choosing Economy Basic for the outbound and Plus for the inbound this gives a total of £185. However - the fare class for the outbound is still N.

Is there any reason I can't book the Basic/Plus combination and then UuA the outbound? As it's still a N class fare I think this should be possible.

If I do this will the extra cash component remain £17 or will this suddenly increase?

I'm fairly certain a basic fare UuA'ed to CE would still have the CE baggage allowance - is this correct?

Thanks for any help!