Deed of Separation - is maintenance payment classed as 'essential expenditure'

[LakesGrandad]

My parents separated about 20 years ago. They had a Deed of Separation drawn up by a solicitor. My dad is making monthly financial payment to my mum. He has recently had a financial assessment done by local authority in relation to him moving into care home, and they say the monthly payment is not classed as essential expenditure when working out his disposable income. Apparently if it was paid under a court order rather than a deed of separation it would be classed as essential expenditure. Will have a major impact on what he will be able to pay towards his care fees. Would appreciate any advice.