I'd suggest you this. http://www.which.co.uk/consumer-rights/action/how-to-use-the-small-claims-court/ but i think that if the amount you claim is bigger than 1000 GBP you can't use small claim court. I think I read that, not sure now.
To get case in to small claim u can go for as low as 75gbp.
Fee for that is 25GBP which in case of full refund u will loose.
If CH will aknowledge the case u have another fee. But most of cases finishes at first stage.
If CH will aknowledge and will insist to go to court u will have other fees as well. But if CH will settle claim without going to small claim court u will loose 25GBP and u cannot claim that form CH. Thats the law. The best thing is, that if CH will not aknowledge within certain time this claim u will get from court by default order to get money back. And from there just simple few steps to recover costs. The fact that their LTD make this a bit difficult but once one small claim court will go ahead there will be more and they will start refund money.
Yes that's the fee to start the process, nothing you can do about that if they force you to go legal.
Page 3 here lists the fees depending on how much you are claiming
http://hmctsformfinder.justice.gov.uk/courtfinder/forms/ex050-eng.pdf
If the are stupid enough to actually go to court then the hearing fee you should get back.
"If you are the claimant and you win your case, you will get the court fees back as well as the claim, and you can ask for certain expenses also. If you lose, you will not get the court fees back. But it is unlikely that you will have to pay any other costs."
http://www.adviceguide.org.uk/england/law_e/law_legal_system_e/law_taking_legal_action_e/small_claims.htm
Even if CH will go to court(which i think is stupid and cost idea) they still can finish case buy settling the claim. They will refund money back but not the costs.