The Irish Fiscal Advisory Council says a spending increase announced as part of next year's budget is not "prudent economic and budgetary management."

In its assessment of Budget 2019, the watchdog finds a Government spending increase of €4.5bn in 2019 goes beyond the limit of €3.5bn for spending increases or tax cuts.

The council had assessed this as appropriate ahead of the budget, on the basis of sustainable growth rates.

It says: "The larger increase mainly reflects the fact that the budget plans for 2019 are built on the imprudent increase in spending in 2018.

"The overall increases also go beyond the Government's own plans set out prior to the budget.

"With the now-higher base for 2018, the underlying increase in total expenditure (net of tax measures) from 2018 to 2019 is currently €1.4bn beyond plans set out in SPU 2018."

It adds that the Department of Finance's own estimates set out in the budget suggested that Government plans would breach the fiscal rules for 2018 and 2019.

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But it says that repeated failures to prevent "unbudgeted" spending increases within the year have left the public finances more exposed to adverse shocks.

"These failures also mean that the budget balance remains in deficit rather than in surplus.

"Failures to prevent unplanned spending increases have meant long-lasting increases in spending that are difficult to reverse.

"These increases represent a repeat of the policy mistakes of the past."

Generally, the council says the pick-up in growth has been driven by a "cyclical recovery" - but that a slowdown is "inevitable".

"The economy now looks to be close to its potential, and the short-term outlook remains strong.

"Yet a slowdown in coming years is inevitable and there are numerous risks.

"Significant overheating pressures could build up if a faster-than-expected, though welcome, pick-up in housing construction materialises.

"On the other hand, Brexit may prove to be more costly than assumed, while the concentration of Ireland's exporting sector, the global rise in protectionism, and possible future changes in the international tax environment also pose risks."