This is the Jetpack mobile theme. To disable the Mobile Theme, go to Jetpack -> Settings -> Writing tab and scroll down to the Theme Enhancements and the “Optimize your site for smartphones” option and turn that off.
Thank you for your response. I had seen a post on disabling the Jetpack optimise for smartphones function and had done that prior to this support request.
I have just checked it and it is definitely disabled. Any other suggestions?