I play blitz on my dongle and have been playing for about a year and have become an alright real life chess player with members of my club no longer treating me like a leper. Which part of my game gets least practise when I play blitz as this is the part of the game I will devote my study time to. I am thinking endgame because winning on time is a major part of blitz strategy. I also think deep tactics are also neglected in blitz. Any help would be much appreciated.

Strategy and endgames.

Planning.

Blitz is 100% attacking and tactics, so there the strategy does not really matter. The endgame is strategy also.
This is why it is harmful to play a lot of blitz games. When you play a chess game, you should practice the full part of the game, not only just attacking and tactics. (and the tactics in blitz is not the same as in a normal game, because you dont have enough time, but you have greater chances for that, your opponent wont see your combination because both player plays fastly in a blitz game)
So blitz is a good game, and you can play it, but mainly you should play normal chess, if you want to get better in real life chess.

I disagree about endgames. Strong endgame players are particularly lethal in blitz because they already know the plan they want to pursue.

The two most difficult features of chess to play well in blitz are defense and fighting spirit.

What I mean is this: if you watch two grandmasters playing against each other in a long game, the winner is often the player who has the stamina to keep pushing for hours on end. This skill just doesn't happen in blitz games where defensive schemes are broken down more easily and it's much harder to resist the flow of the game. After all, if you lose a blitz game, just set up the pieces and start over. The stakes of the individual game are much lower in blitz than in longer games.