I came across this rather interesting blog which gives detailed installation instructions on how to install Windows 10 TP to a VHD.
http://hyrokumata.blogspot.co.uk/2014/10/installing-windows-10-technical-preview.html
I found it interesting as it introduced me to the world of VHD’s and also worked 1st time.
I now have a triple boot scenario of W7/W8/W10 without having to create a new partition for W10.
I’m pretty sure there are other ways of accomplishing the same thing, if you know, please share!