Glasgow Airport is to invest more than £3 million extending one of the airport's three piers, allowing more passengers to board planes without stepping onto the asphalt aprons.

The upgrade - planned before the recent sale of the airport - was largely caused by the need for extra capacity following Ryanair's move to Glasgow from Prestwick.

Although the east pier currently has stands for eight aircraft, passengers can only board planes directly from three stands. Other passengers - often those flying with budget airlines such as Ryanair - currently have to be taken by bus or walk out to their aircraft.

The new 1400sqm, two-storey ­extension will allow more passengers to board planes directly from the gates. Construction work is expected to be completed by next spring.

The decision to extend the east pier follows Ryanair's announcement earlier this year to establish its 69th base at Glasgow Airport.

This led last month to the transfer of some routes from Prestwick to Glasgow, in a move expected to increase passenger numbers using Scotland's second airport by 850,000 a year.

Other new routes to be launched next year - to Halifax, Nova Scotia, the Cuban capital, Havana, and Bordeaux - mean that passenger throughput at the airport is expected to exceed eight million for the first time since 2008.

Glasgow Airport was last month sold by the Heathrow Airports group to a Spanish and Australian consortium comprising Ferrovial and Macquarie. The £1 billion sale also involves airports in Aberdeen and Southampton, and is expected to be completed by January.

Amanda McMillan, managing director of Glasgow Airport, said: "This latest project brings our total investment figure for the year to £20m.

"This new extension will significantly enhance our facilities and improve the passenger experience for the millions of people who travel through our doors every year."