If you have a credit card, you could just buy £500 of stuff instead. You could buy 24,000 miles and leave 23,000 for your next redemption. You could not make the redemption and buy a ticket instead.
Just speaking personally, my redemptions have been sufficiently swanky that I wouldn't have been fussed by an extra few pounds here or there. On the other hand, I would happily shop around or change travel dates to save a similar amount on domestic leisure flights.