OP - I set out the ACAS commentary below. From which it seems that compassionate leave is determined by your contract (or employer’s discretion, I guess, if contract doesn’t provide for compassionate leave) but that you can exercise your statutory right to depandant leave
“Compassionate leave: Taking time off for a bereavement
When someone close dies, the last thing most people want to do is trawl through their contract of employment to see whether they are entitled to any compassionate leave. Neither would most people relish the prospect of an awkward conversation with a line manager, having to explain who died in order to justify a short period away.
All employees are entitled to 'time off for dependants'. This is a reasonable amount of unpaid time off to deal with unforeseen matters and emergencies involving a dependant, including leave to arrange or attend a funeral. A 'dependant' could be a spouse, partner, child, parent or anyone living in the household. It could also be someone who relies on an employee for their care or for help during an emergency, such as an elderly neighbour.
But what if the deceased is not a dependant? Many employers do have a policy for compassionate leave, which employees can find in their contracts or company handbooks. Experts maintain that writing paid compassionate bereavement leave into a contract can be a major support to employees, and have a long-term positive impact on their relationship with employers. Having a scheme in place is also helpful for managers, who can fall back on written policy and are spared the ordeal of having to assess the seriousness of the situation themselves.
Without such a scheme, it is up to employers to use their discretion, being as reasonable and as consistent as possible. Managers will have to have an eye on what the custom and practice has been in the past and apply precedents fairly and consistently. Even so, employees cannot expect to be granted leave automatically. When leave isn't granted, they may have to use their holiday allowance.
Acas can give advice on Bereavement in the workplace and all aspects of leave-taking, including Time off for dependants. Acas also offers training courses on Human resources management for beginners, which covers how to deal with leave procedures.
Visit the Acas Training Courses, Workshops and Projects area for more information.”
I hope this gives you another avenue to look at