Thanks Abi, I’m glad you found it useful!
For your question, it’s worth checking if you mean UK-wide, England, Wales, NI or Scotland as they all have separate indices.
It’s worth reading the guidance to understand how they work before you get stuck in.
Index of Multiple Deprivation for England (2015)
You can contact the Ministry of Housing, Communities & Local Government by email (indices.deprivation@communities.gsi.gov.uk), they may be able to advise what constitutes an area being declared most deprived.
Index of Multiple Deprivation for Wales
Index of Multiple Deprivation for Scotland
Index of Multiple Deprivation for Northern Ireland
Please add your reflections and findings to Resources for check-in #1 - Finding Data.