The quickest way to end a LDR is to be overly pushy on the other person's time, to demand attention and to make them feel bad/guilty/whatever about spending their time living their own life, is to be needy.
A LDR requires more than twice the amount of trust that one that occurs in the same room has. You need to be absolutely sure in your own motives, the motives of your partner and in the situation. If you aren't, your relationship will self destruct pretty quickly, and the more you push for more time and attention, the quicker it will disappear.
If he's not online you need to be happy that he's out living his life, seeing his friends, watching TV, playing games and having a full social life. He should be living a happy life full of fun and friends in the UK, if he loves you, he'll always come back to you when he's free. You need to be doing the same, take up a hobby, go out with your girlfriends, go shopping, have a long bath with lots of bubbles, don't sit around thinking of how late he is, or that he hasn't called. Live your life, then whenever the phone rings or an email pops up, it has no negative connotations, it's just an unexpected pleasure.
Love is not measured in the amount of time you spend on Skype, nor the number of emails you receive, it is measured in the depths of your hearts. Either you trust that his heart is deep and you accept that he has a fun/important/worthy life he needs to live outside of your relationship or you spend your time trying to gauge "signs" from the number of words he types.