Work will begin later this month on a £30m expansion of Scotland's busiest airport which will reduce security waiting times and significantly increase capacity.

The major development at Glasgow Airport, called Skyhub, will lead to the international and domestic departure areas being combined, with travellers passing through a single security zone.

It will be the biggest single investment by British Airports Authority (BAA) in Glasgow Airport for a generation.

However, the expansion could result in a trebling of passengers which would be disastrous for the environment, according to campaign groups.

Improved shops, bars and restaurants are planned in the departure lounge.

Glasgow Airport deals with 8.9 million passengers a year and serves as the country's long-haul gateway to the US, Canada, Egypt and others.

Gordon Dewar, managing director, said: "We want to make the journey through Glasgow Airport as safe, smooth and enjoyable as we can for all our passengers, delivering better service not just for today, but for the next generation of travellers.

"Skyhub is the biggest single investment by BAA in Glasgow Airport for a generation and underlines BAA's long-term commitment to the airport."

Work will start later this month on the two-storey development, which is expected to be completed in 18 months.

A single security check area will replace the existing three zones, freeing up space for shops and other passenger facilities.

The new search area will have capacity for up to 14 X-ray machines, four more than at present.

Mr Dewar added: "This expansion will allow us to concentrate our security search areas in one location, freeing up a huge amount of additional capacity within the terminal.

"This is particularly important during the busy summer months when Glasgow Airport can expect to handle over one million passengers in a single month."

Kirstie Shirra, head of Scottish campaigns for the World Development Movement, an anti-poverty campaign group, said the airport expansion would be a disaster for both people and the climate.

She said: "Plans to treble the number of passengers at Glasgow make a ridicule of the UK's efforts to tackle climate change. Aviation expansion must be halted if we are to have any chance of reducing our climate emissions. The plans for expanding Glasgow Airport should be scrapped."