I went the route you are describing, did my CPL then FI, instructed for about a year before I completed my MEP and ME-IR and it all worked out really well.
Many of the people on my original course got their CPL-ME-IR and then sat on it for a year before giving up hope and getting an FI rating to build their hours, by which point I already had more than triple their flying time.
Instructing is great fun, and if you really want to teach and pass on your knowledge then it's the best place to be. If you're purely after the hours then look elsewhere, or you will get incredibly frustrated with the British weather.