Your home is well proportioned and well presented, a really lovely family home. It's hard to say without knowing the area well but I think for that kind of money, I would want better carpeting in the bedrooms and I'd want the lounge to be better decorated (it's nice but nothing too special for over £1mil).
I'd also want the windows to be uniform and personally I don't like the stripey hall carpet either although appreciate that's a personal taste thing.
I would also landscape the garden more. Get a professional in who can make it look special.
I love your kitchen extension area and the loft room.
You're asking for a LOT of money, which most people can't afford. So you have to appeal to the relative few who can, and I'd imagine for that kind of money they want it to be special, packed with good quality, innovative features.
Who is your target audience? Local families upgrading? (Although how can they afford that?) Or families moving out of more central London with large budgets? If that, then you've got a lot of competition from the home countries where £1mil + will get them much more land and a detached property.
Think about your target audience and cater to them.