Originally Posted by
corporate-wage-slave
Yes, this is going back a few years, but for some reason UuA when bought straight up are charged against Plus fares, but thereafter you can UuA against Basic too provided it's N or above. So buy the Basic fare online, get the e-ticket, then UuA. If necessary you can call within 24 hours and fix anything without additional charges or even get a full refund.
And it will get the CE baggage allowance.
Thanks so much for your advice as always CWS! Can confirm I was able to book the basic and then immediately UuA it for the extra Avios + £17 and the CE baggage allowance is now there.