do I have to declare these for ctc or tax purposes

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Hi, we are expecting a large sum from an inheritance in next few weeks and some compensation for an accident claim later in year, approx £30-40k.

Does anyone know what we do and do not have to declare?

no

Money received from an inheritance is usually taxed before it is distributed. But you can read this explanation from HMRC in more depth Tax On Inherited Money Compensation for personal injury is not usually taxable.

For tax credits you will have to declare any interest over £300 that you make on it, but not the actual sum AFAIK