Ryanair has reduced its full year net profit guidance by five per cent as the value of sterling continues to fall.

The low-cost carrier cut its forecasts from a previous range of €1.375-€1.425 billion to a new range of €1.30-€1.35 billion earlier.

The primary cause of this slightly lower growth in full year profitability is the 18 per cent fall of sterling post Brexit, the airline said in a statement to markets.

As a result, Ryanair will reduce average fares by between 13-15 per cent in the second half of the year, as opposed to the previously guided 10-12 per cent.

Ryanair confirmed that its first half fares were marginally weaker, down ten per cent, compared to previously guided fall of nine per cent.

However, these lower fares will be partly offset by a better than expected cost performance.

Ryanair chief executive Michael O’Leary said: “The recent sharp decline in sterling post Brexit (which accounts for approximately 26 per cent of Ryanair’s financial year 2017 revenues) will weaken second half yields by slightly more than we had originally expected.

“While higher load factors, stronger traffic growth and better cost control will help to ameliorate these weaker revenues, it is prudent now to adjust full year guidance which will rise by approximately seven per cent over financial year 2016, rather than our original guidance of 12 per cent.”

Ryanair now expects full year ex-fuel unit costs to decline by three per cent compared to previously guided one per cent.