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If you die without making a Will, your Estate will be distributed in accordance with the strict Rules of Intestacy. So, while you are still married, albeit separated, your husband is still seen as your legal next of kin and the first £250,000 of your Estate would pass to him.
I set out a link expalining in detail the full Intestacy rules.
I would of course suggest that you make a Will!
I hope ths helps and answers your question.