I regularly buy One Day Travelcards in advance each day for the following week, but have since changed my plans and no longer need the ticket for the day after tomorrow (London Terminals & London Zones 1-6 with a DSB railcard for £5.60). Having taken it back to St Pancras today (the ticket office I bought it from), I've been told that the £10 admin fee still applies. I thought that the fee didn't apply if the ticket was surrendered before the date of travel, and as a former BR employee in the 1980s and 90s, that's what I used to tell the passengers back then...