Occupation rent and third parties

In the process of divorce after 20 years where I worked and financed everything. I remortgaged my flat to buy a house which we lived together in for 4 years on an interest only loan. I am planning on moving back to the flat which was rented out, very soon as he refused to move out despite his ongoing adultery. I read that he could be ordered to pay me an "occupation rent as I now have to pay a very large mortgage on dwindling savings and am currently unemployed. Does anyone have any experience of this and can it be backdated??
I also read about Third parties where a court does have the power to require a third party to attend with documents that can be inspected and wondered if I could request his new partner of 2 years be asked about her finances? I know she has her own house worth 400,000 and no mortgage as well as a reasonable income.
Any advice would be very welcome.
Thanks

I''m afraid I don''t have much experience on the subject of occupation rent.
Can you establish certain facts for me ?
This flat, is it in joint names ?
Am I right in thinking that there was a time when you occupied it together and then you moved out ?
And subsequenly to your moving out he moved his new partner in ?
Do you know if he has registered matrimonial home rights against the flat ?

As a general rule, if you are the sole owner of the flat, he, as your husband is entitled to live there by virtue of the fact that he is your husband. These rights will normally terminate on divorce ( as he would no longer be your husband ). It is possible that he could apply for an order giving him the right to continue to live there at least until the finances are settled. However the fact that he has a well heeled partner would clearly count against him ; it would seem on the basis of what you say that they are quite capable of housing themselves and are using you as a convenience.
The fact that he has a new partner is relevant ( in principle at least ) to his future needs. You can certainly ask about the new partner''s resources but I''m not clear about whether the NP has any obligation to disclose her assets, even though you have no claim against the NP directly. Those resources are only relevant to the extent that they affect his needs.
But there are always dangers, from his point of view, that if the NP does not disclose her resources, the Court may make assumptions and act on them, and the Court may make a more severe order than it would have done if they had all the facts.
I am afraid that this will call for legal advice which I do not feel able to give you except in general terms.
LMM

Thanks for your help and input. I will discuss with my solicitor but aware every time I go to her for advice it costs me and my money is fast disappearing.