No, that £1 to £5 applies if you're among the first ten to book tickets on that flight. They use a bucket system where the first ten tickets are really cheap, the next ten a little more expensive, etc, and the last ten rather expensive.

I don't think the actual bucket size is ten. But I'm fairly sure that they hope to sell more tickets from the later, more expensive buckets, not from the earliest buckets. They don't plan to fly many almost-empty flights.