Proof of mental incapacity required by court

[Angie1]

When mental incapacity is claimed, would a claimant have to provide the court with an expert medical opinion, or would documents extracted from the patients psychiatric medical records that prove mental incapacity suffice.

[bobjugs12]

In what context?

[Angie1]

As a personal representative Im considering bringing a claim for breach of contract.
I will be acting on behalf of an individual who lost mental capacity.
I know the burden of proof lies with the person claiming mental incapacity, but I have been quoted in excess of £1000 for an expert medical opinion.
Am wondering if the court would accept proof of the incapacity in the form of documents extracted from the patients psychiatric records instead that clearly show mental incapacity at the time in question.