The first place to look is the Employment contract. This will often contain a clause on 'compassionate leave' which sets out any employee entitlements in this regard - including how much time can be taken off work and if this will be paid. Alternatively, a Bereavement leave policy may set out a business' approach towards bereavement leave.
Under the law, employees are legally entitled to 'reasonable' time off work to deal with emergencies, including bereavement involving a dependant (eg a spouse, partner, child, grandchild, parent, or someone else who depends on the employee for care). What is considered a 'reasonable' time off is not defined - and will therefore depend on the specific circumstances. There is no legal requirement for an employer to pay an employee for time taken off work due to a bereavement.
Furthermore, employees who experience mental health difficulties following the death of a loved one may - in certain cases - be considered disabled for purposes of the Equality Act 2010. In such a case, employers are required to make reasonable adjustments.