get a BA Amex, spend 10k to earn your 241 voucher, book an open jaw F return using all 150k miles, or if you want to save some then J out and F back (but then you'll miss out on the Concorde Room in T5 and as its your honeymoon I'd go F both ways).
Looks like you have to spend £20k to get the 241 voucher:
http://www.americanexpress.com/pes/u...mpare_ba.shtml