Yes, as Rubecula says it has to be 30 days prior to the flight, has to be done by phone, can be refunded up to 24hrs beforehand incl. taxes/fees (i.e. no £35 charge) and you have a decent chance that they will forget to take the multiple to double the avios, but they may decide to do so at any time so if you don't have enough avios in your account to cover it you may lose your booking.