The ex has changed the locks to the house for the second time, I still pay the mortgage and all my clothes and personal things are still in the house. She is refusing to allow me to collect just a few of my things, as I don’t have nowhere to store all of it.
She is going to her parents for Christmas.
Can I gain access via a locksmith and take my things from the house?
As I understand it, whether you are paying etc is not the point: she has a right to privacy in her own home.
I had been advised not to change the locks though. Luckily my ex handed his keys over without being asked (though I was never sure if he had another copy). When it was clear he wasn't coming back, I could have changed the locks, but I never did.
After a couple of years, in which I had returned everything he asked for and more (allowing him in to help himself at first) when I had to sell up and move out with the children, I arranged with him a day when he could collect those belongings that had been in the loft etc, and I left them outside the house. I no longer wanted him in what was then my home, though he co-owned it. We were embroiled in a divorce and I didn't want him to have access to my papers or computer.
Perhaps you could ask your ex to please leave your things somewhere for you. You may want to list particular items that you want, as well as having a catch-all phrase to cover the rest of your stuff. You may need to ask a friend or pay for storage for some of it, but I would take it all, so you don't have to renegotiate in future.
I wouldn't issue threats about essentially breaking in as that will likely only rile her.