The first place to look is the Contract of employment. 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.
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.