If the Irish economy is losing €600mln in tourism revenue, the VAT on this loss will likely be ca €80-100mln (as some services bear reduced VAT). This is the first round of losses to the Exchequer.
But every euro spent by a tourist in this country goes to pay for goods and services here, which in turn generates banks deposits and payments to suppliers. These payments are then used to generate new economic activity, thus triggering a second round of tax receipts. And the merry-go-round then goes on to the third round and so on.
Given the average OECD private spending multiplier is approximately equal to the M1/M3 multiplier, which is roughly 3.8-6 (depending on the range of years chosen, with the lower number coincidentally referring to the years of the most recent global markets boom), then these losses are indeed much greater than those claimed in Ryanair note.
Back of the envelope calculation suggests the Exchequer will be foregoing some €120-250 million more in revenue on top of the first round losses. And this is before we factor in income taxes and other taxes, such as charges on fuel that foreign motorists might pay while touring Ireland.
So we are now back to the old equation: put a €10 tax in place, lose some €100-230 million in revenue. Good luck running the country with these mathematics...
Note: that article attacking my and Ryanair analysis of the travel figures that predicted the yet-to-materialise substitution effects of Irish travel tax is available from the Irish Times site (here).