Ben Plowden, chief executive of lobby group Campaign for Better Transport, said: “Today’s inflation figure could mean a big fare rise for rail passengers next year, especially if the Government decides to go with an above-inflation increase like we saw this year.

Economists expected inflation to rise to 3.7%, though the Bank of England forecast for July inflation was 3.76%, slightly higher than consensus. Inflation in the UK has risen to an unexpected 3.8%, the Office for National Statistics says.

Train tickets could become 5.8% more expensive next year, affecting about half of rail journeys, after the Retail Prices Index (RPI) measure of inflation for July came in higher than expected.