Sorry to anyone who tried to buy a signed hardback and was charged £20 instead of £15. The problem has now been rectified. The Warhorses book (and print, mug, embroidered horse blanket, pony trekking trip etc) can be found here.
(I’m assuming none of you actually paid £20 for a £15 signed hardback (unless you’re outside the UK and paid £5 for postage) but if you did please let me know.)