Hi there! My name is Greta (from Texas). Most of the Websites and Applications we build are WP based Custom themes and Plugins. I have no doubt that I can assist you in creating both “from” scratch themes with theme-options panels, as well as completely customizing existing themes (either turning them into a “new” theme” or creating Child themes). In addition, I have built extensions and add-ons, and implemented custom integrations for popular plugins, Woo-Commerce, Gravity Forms, etc..
I realize that your preference is for UK based Freelancers, however, I spent over 5 yrs based out of London (Shell Expat -made a career change) and there is no “time difference” when deadlines are in play.
I develop on my own servers, so the websites will be built in a live environment. When ready for “launch”, we port over the database and file structure (typically a 2 hrs). The advantage is that the complete website can be reviewed by the client before going live. For custom plugins and themes I have an updater script which enables “Updates” to the live sites admin panels just like standard WP which would make it more intuitive for your customers.
Rates: Typically 150-300GBP for Existing Theme Changes 250-600GBP for complete custom to full implementations. Custom Add-on or Plugin development will need to be qtd separately based on requirements. My Skype user name is Troobles, so if you are interested please let me know what time you would like the initial chat. Warmest regards, Greta