AS the letter says you will get CB ESA for the time stated then if you satisfy the [strict] means test you can then go onto claim IB ESA. However, if you do not pass the means test then you will have to live off the household income that is coming in. Please see the ESA guides which explain the differences between IB ESA & CB ESA and the implication of time limiting CB ESA. The time limiting rules do not apply if you are placed into the Support Group of ESA.
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