I've emailed John Lewis and am waiting for a reply, I'm just wondering whether I might have missed something.
When I adjust the seat to the highest position then put my small toddler in it, the weight of him pulls it straight back down to the smallest setting again. Has this happened to anyone else, is this a design fault or did I miss a clip to hold the seat in position in the box? 
It's ok at the moment, but as he grows he's not going to fit under the hood.