In addition to Globaliser's comments, if using a 241 I don't see the savings by only using it for a one way and buying or using avios (and paying the ex-eu surcharges) for the return. Also see these threads:
Taxes and Fees on 2 x 1 way vs 1 rtn
RT Fuel Surcharge Greater than Sum of OWs
Carrier imposed charges 2x if buying round trip from US
Chase BA Companion Ticket $30,000 Spend