Budget airline Ryanair saw its shares hit an all-time high this week after a drive to improve its image helped attract a million extra passengers last month.

The Dublin-based carrier, which is the largest operator out of Stansted Airport, said passenger numbers in December jumped 20 per cent on the year before to 6.02m.

Its load factor – the aviation industry measure of how full an operators’s planes are – increased by 7 per cent to 88 per cent over the last 12 months.

The surge follows a drive by Ryanair to improve customer service by softening its stance on baggage charges and booking conditions after suffering two profit warnings at the end of 2013.

Its shares lifted more than three per cent on the Irish stock exchange yesterday and have jumped 59 per cent over the past year.

Over the 12 months to December the airline, led by chief executive Michael O’Leary, said passenger numbers lifted six per cent to 86.4m.

Ryanair’s chief marketing officer Kenny Jacobs said the airline was benefiting from its Always Getting Better customer programme as well as lower fares and stronger forward bookings.

In August the carrier introduced its business class service, called Business Plus, which includes flexible tickets, priority boarding and premium seating. The moves came after budget rival easyJet built up a sizeable business class base over recent years by selling additional services.

Last May Ryanair unveiled annual post-tax profits that were 8% lower at 523m euros (£408m) after a price war left average fares 4% lower at a time of rising fuel costs – the firm’s first drop in annual profits in five years. However, in November, as demand increased, it said it expected annual profits of up to 770m euros (£602m), an increase of 18% on previous guidance.

The airline operates more than 1,600 routes from 68 bases across Europe. Last summer Ryanair launched 57 new routes and added four new bases in Athens, Brussels, Lisbon and Rome.

A new contract signed with Stansted Airport following its acquisition by Manchester Airports Group in 2013 has been a factor in the Uttlesford airport’s return to passenger growth.