Forcing House Sale

[paulo21]

I jointly own a house with my ex partner who has 2 children from a previous relationship aged 6 and 16, I have no children.
We bought the house for 200k in Feb 2008, we bought the house from her dad for 25k less than the valuation of 225k - the 25k effectively worked as our deposit on the house.
The market dropped, but i personally built an annexe to the house, so increased the value of the house significantly, it is now valued at around 235K.
I moved out of the house in March 2009 as me and her werent getting on well, and moved in with my parents. She has remained in the house and has been paying for the mortgage since I moved out which we agreed to as we had a great deal on a tracker mortgage so was costing her next to nothing.
I wish to sell the property, but she doesnt want to can i force a sale through applying for a "order of sale"? If i were to do this as i own 50% of the property am i likely to get 50% of the sale price - with her having 2 children?
Any response will be very much appreciated!
Thanks

[paulo21]

sorry forgot to add, to put in the same amount in for the development works on the house and also the legal fees etc on the purchase

[buildersmate]

Is your name on the Land Registry land title for the property and also on the mortgage?

[paulo21]

Hi thanks for responses my name is on the land registry land title and the mortgage, I havent paid anything towards the mortgage for 12 months. She changed the locks and hasnt let me collect my stuff, plus she has let the annexe which has been bringing in £500 per month and she has been paying the mortgage of £165 per month.