Maintenance increase

[sleepingwiththeenemy]

Hi. I have been divorced from my first husband for 7 years now, and we had a court order in place for him to pay £300 per month for the 2 children. BUT...in 7 years, despite the fact that his salary has increased and the children have got older (and therefore more expensive) his payments have never increased. I'm a single Mum, have 3 kids and struggle on the money I get. He doesn't contribute to clothes, school trips etc, and when he sees the children in holidays I have to do the journey one way which costs £50 in petrol each time. So...can I ask for the payments to be increased? Should he pay towards school trips etc on top of maintenance? And how much, given the 7 years of salary increases, should I reasonably ask him to pay? He lives with his girlfriend, they both work full time and have no kids.
I think I'm going to have to ask him to pay for the petrol to see the kids, and to top up the money I get. As it is my 13 year old daughter has next to no clothes, and I panic every time a school trip comes up. He knows we are in a dire situation as I had to flee my 2nd marriage as my husband sexually abused our baby daughter, as well as me and was emotionally abusive towards the children. At the moment we are 'in hiding' far from home, and staying with a friend who is in no position to financially support us, and we are due to move into our own council place in the next few weeks.
Any ideas? Suggestions?

Hi, and thanks for the responses so far. I'm sorry to anyone who thinks I came across as lashing out; it certainly wasn't meant and I do apologise. With all that is going on at the moment I am ultra sensitive. It probably seems like I am trying to make ExH pay more to make up for not being able to claim anything for DD2, but that's not the case at all. As I haven't asked for an increase in line with the cost of living rise,and wage increases every year,I simply felt that - at such a difficult time when me and the children have left everything behind to be safe and to start a new life away from the monster I married second time around - that the children's Dad could either increase the maintenance by, say, £50 a month OR pay the petrol when he sees the kids. DD1 has been at his for the last few days as the whole situation is taking it's toll on her and she needed to get away; I paid £52 in petrol 2 weeks ago to pick them up from there, the same at the weekend just gone, and all I asked was that he paid the return petrol. I even drove to get her today, just asked him to leave the money for me and he went berserk...when I got there he ignored me, and wouldn't speak at all! I don't think I'm being unreasonable at all. He just fails to see that the children are OUR responsibility and we should make joint 'sacrifices'...he actually said that he can't 'turn on' being a Dad outside the times he would normally see them i.e school hols, and that I had been unreasonable asking him to look after her at the weekend to give her a break from the ongoing s**t.

It didn't come across to me like that to me . And I'm at not being able to "turn on" being a Dad, and it's unreasonable that your dd goes to him at the weekend . Says it all really.