Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Did you protect your investment with a Declaration of Trust when the property was purchased?
The problem is that it is about what was agreed at the time - not how much you each actually paid.
Did you ever discuss what would happen if you separated?
Sorry - I meant at the time that you purchased the house together?
In the absence of any other agreement it is assumed that the property will be held in equal shares.
You can argue that there is no basis on which you intended to "give"your ex the extra £4,000 (the difference in your capital contributions if they are split equally between you) but I am afraid
it is unlikely that the unequal mortgage payments can be reclaimed.
You can read the basics here
http://www.mills-reeve.com/commonlawmarriagemyth/You ned to try and negotiate with her using Family mediation - a 70/30 split is too high - aim for 60/40.
Please be aware that once the sale is over you will have no basis whatsoever to claim any extra payments
Please ask if you need further details