This is one of those US/UK differences. In the US, we usually refer to companies or groups (like sports teams) as singular. In the UK, companies have been historically referred to as plural. Since the parent uses the British spelling 'favour', but feels the singular form is correct, I wonder if that's changing.
If we're referring to HP as a collective of things (i.e. individuals, such as the board) then it should be have ( - they have ....)
IMO I'd say it could be either really, though I would probably favour the singular.