A 2014 Cube Agree GTC (carbon) can now be had for £799 with full 10 speed Shimano Tiagra, a 2014 Giant TCR Advanced or Defy Advanced (both carbon) for about £899, all are definate upgrades over your Defy 5.
The Best upgrade IMHO is the 2015 Canyon Endurace CF, lightweight Canyon carbon frame & forks with full 11 speed Shimano 105....
you would have to stretch to £1099 for that one, but it is an absolute steal for the money.