When performing the duties of an executor he must “exercise such care and skill as reasonable in the circumstances”. This is set out in s1 Trustee Act 2000 - which pre-dates this situation.
A breach of duty by an executor is called devastavit - try Googling it - you might find out more. It splits into two types - misappropriation and maladministration. What you are referring to could be either.
Maladministration occurs when funds have been misapplied, - distributing assets to
persons not entitled, paying unjustified expenses and wasting the value of assets.
If devastavit is proven, the executor is personally liable for any loss. However,
there are a number of defences available, for example, an 'exoneration' clause in a will may restrict an executor's liability.
Under s22 of the Limitations Act, beneficiaries can bring an action within 12 years from the entitlement date, however this does not apply if fraud is involved.