i have just had a letter from CRA with regards to a 2014 t1 return,we left canada in november 2013 but are returning in 2016 , am i wrong in thinking this is for the year 2014 that is filed before april 2015 so should we have still filed although we were in the uk all that year or does it mean the tax return for 2013 that is filed in 2014.can anyone answer this for me

When you filed your 2013 you should have ticked the box to say that you left Canada during the year and give the date. If you did not do this the CRA don't know you left and are expecting a tax return for 2014.

The simplest solution is to write back to the address the letter was sent from, explain that you left Canada in 2013 (and give the date) and tell them that you were living in the UK for all of 2014 and 2015 where you were taxed by HMRC as a UK tax resident (as long as that is true). There is no need to mention that you intend to return in 2016 unless asked. Hopefully the CRA will accept this at face value. They may reassess 2013 if you have claimed your personal amount for the full year.