Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"Second point -- I don't think OP has any Avios in stock."
True. But that's real easy to fix between now and July: Chase Sapphire Preferred card; Chase BA card; Amex SPG card; or any Amex card that participates in the Membership Rewards program. (Of course, just taking the Eurostar from LON to PAR might be a more convenient option.)