My seven year old has been to a couple of Nerf gun parties both indoors and outdoors. You have to arrange the venue, but they come to you. The outdoor one he went to had inflatable tanks and an obstacle course they had to navigate. All the bullets are foam and do not hurt.
Or you could try a go-karting party in Surbiton. http://www.surbiton-raceway.co.uk
We've done this and it is really good fun but it means guests have to schlep out to Surbiton. In my view, it's worth it as it's a proper go karting course.
Or you could consider a laser tag party. I think lots of places, including Eddie Katz offer this.