I've had this happen a few times with multi-passenger hold bookings - when you pay for them during the hold period, the passenger names get all screwed up and end up using template names in the same fashion as you describe. I'm guessing this is something to do with the change from a hold booking (where passenger names aren't stored) to a confirmed booking (where passenger names are required), and things get a bit broken for a bit. However, in every case I've seen this, after anywhere between 15 minutes and a few hours, the booking sorts itself out and all is well - when the booking is in this "slightly screwy" stage you may also find that you can't change seats (even if entitled to by status), and/or can't email the e-ticket receipt etc.

So fingers crossed, by the time you read this, your booking will have sorted itself without further intervention - though if it hasn't by the time the UK call centre opens on Saturday, probably worth giving them a call just to double check that all is well.