I've checked our NHS policy, and the policy says that managers and employers should encourage people to take their full holiday allowance (in the interests of employee wellbeing) but there is no insistence - you just lose your holidays if you haven't taken them all by the end of March. In the current climate, there is no way you'd be paid to stay at work rather than take your hols. No way either we can take unpaid leave unless in an emergency - we are needed in the office, not enough staff already, and there is nobody to cover our work when we're away.