Hi again Peter,
Thanks @darren-white for pitching in.
It means 80% of their average annual earnings as you laid out (52 week average) used to calculate holiday pay etc.
It is obviously a higher sum than say their average base salary per week, and perhaps you can negotiate an arrangement in the interest of keeping your business going during this time that you apply the other rate. It is all up for negotiation during this time as long as the employer is communicating, giving an opportunity for feedback, and being seen to be fair and reasonable.
It is also fair and reasonable for an employer to want to stay solvent, so asking an employee to accept the lower rate for now is worth asking in my opinion if it is the difference between viability of your business 12 weeks from now.