If an employee cannot work (i.e. not essential and cannot work from home) do we presume that 'otherwise working days' are determined by pre-COVID lockdown work patterns?

Yes. Determining whether a day is an 'otherwise working day' should be based on the employee's pre-lockdown working pattern. However, if the employer and employee have agreed to a permanent change, this new arrangement can be used to assess whether the day is an 'otherwise working day'.Employers claim the wage subsidy based on the number of hours an employee would work in regular circumstances. Employers commit to paying 80% of wage but if this is not possible they are required to pass on the subsidy in full. If your employee's usual wages are less than the subsidy, you must pay them their usual wages. Any difference should be used for the wages of other affected staff. Any employment obligations between the employer and employee still apply. Minimum wage requirements continue to apply to any work performed or leave used.