It’s best to work collaboratively with your employees with a view to agreeing working patterns which could include taking some unpaid leave or using up holiday days. The new provisions on furlough leave could also offer some important options for employees to consider.
This is a complex and very unusual situation so you should make sure you have specialist legal advice before you take any major steps.
If you do think you need to make people redundant, you need to check the terms of your employee contracts. There could be an express or implied right to lay people off or place them on short time working, which might be triggered in this situation.