Help with housing costs - Partner in prison
If your partner was the one claiming benefits before, and they are no longer entitled to the benefit, you will need to make your own claim for help with your rent. Most people will need to claim Universal Credit, unless they fall into one of the groups who cannot claim Universal Credit.
You will also need to make a claim for Council Tax Support
If you live in a mortgaged property, see if you are entitled to Support for Mortgage Interest.
If you were already claiming these benefits, then you should notify the relevant benefit office of the change in your circumstances as this may change the amount you are entitled to.
For Housing Benefit, you will still be treated as a couple if you plan to live together again once your partner leaves prison, and he is expected to be in prison for less than 52 weeks.
For Council Tax Support you will still be treated as a couple if you are only temporarily separated
For Universal Credit you will be treated as a single person while your partner is in prison, but your income and capital will still be assessed as if your were a couple. If your partner is expected to be away from home for more than 6 months, you will be treated as a single person.