VAT on another tax?

Sir, – I note that on my electricity bill the public service obligation (PSO) levy is added to the electricity charges and then VAT is applied to the total. The Value Added Tax was conceived to apply a tax on goods or services in a progressive manner each time they changed hands until the final customer or end-user. But what good or service does the PSO levy represent? Surely the PSO should be charged to the total after application of VAT? – Yours, etc,

GEORGE REYNOLDS,

Blessington, Co Wicklow.