As a rule prisoners while in prison or on remand do not count as an adult living in a property for Council Tax.
Council Tax Exemption and Reduction:
Single Persons - If you are single and in prison or on remand with no one living in your home you can apply to be exempt from Council Tax.
Note: Your home is not exempt if you are in prison for not paying Council Tax or a fine for not paying it.
Couples (on remand) - If your partner is on remand and expected to be home in a year or less you can apply (or continue) to get joint Council Tax Reduction.
Couples (in prison) - If your partner is expected to be in prison for 13 weeks or less (including any time on remand) you can claim (or continue) to claim joint Council Tax Reduction.
If your partner is going to be absent for more than 13 weeks and you are the only adult in the property you will receive a 25 per cent discount off your Council Tax bill.
You may be able to apply for Council Tax Reduction if you do not already get it.
Prisoner Council Tax Exemption and Reduction; UK Rules Updated 2017