I am an experienced British writer, who would love to help you with your manual. It's difficult to map out an exact strategy, without more information about the topic the manual would cover, however, generally, I would seek to break it into chunks and deliver it piece by piece, ensuring that we ended up with something that matched your exact needs.
In terms of suitability, I feel that my profile speaks for itself, nothing but five star reviews and a rehire rate that is twice the average, before doing this I worked in British politics, taught and studied philosophy. I would be more than happy to provide samples and discuss things further if you get in touch.