No – it is not okay for any employee to work for equity only. All employees in the UK should be paid at least the National Minimum Wage or National Living Wage (depending on their age) for all of their working time (including, for example, any overtime and potentially, any time spent “on-call”). Individual employees can bring a claim against their employer if they do not receive the National Minimum/Living Wage. HMRC may also take enforcement measures including issuing notices of underpayment, civil penalties, "naming and shaming" employers, recovery of underpayments through the courts, and criminal prosecution.
Learn More: UK Founder Series: Building Your Team