FEW airports are more loathed. Fewer still are more vital to the Scottish economy.

For decades Scots have had a love-hate relationship with Heathrow, the London hub that remains the nation's gateway to most of the world. Now passions look set to rise again.

Britain's aviation regulator yesterday announced that it would allow the airport, one of the world's biggest, to almost double its landing charges over the next five years. That, warned airlines, will mean higher fares.

More than 3.3 million people fly between Scotland and Heathrow every year, more than to any other destination. Just over one in six people who board a plane in Scotland are Heathrow-bound. Many are going to the south-east of England. Others are heading for one of the 180 destinations on offer from the London hub. Wherever they're going, passengers will have to pay more, according to most major airlines.

British Airways accounts for most of the 500 weekly flights between Scotland and Heathrow. It said the decision to allow Heathrow's owner BAA "to ramp up airport charges significantly demonstrates conclusively that the airport regulation system has failed".

Four other operators - Virgin Atlantic, bmi, Ryanair and easyJet - said the regulator, the Civil Aviation Authority, was "not protecting the interests of consumers" and that it should be breaking up BAA's near monopoly over major London airports.

The CAA tightly regulates pricing at the five London airports, three of which - Heathrow, Gatwick and Stansted - are owned by BAA. The watchdog's latest ruling will let the Spanish-owned BAA hike charges by almost 100% at Heathrow and by around 50% at Gatwick over the next five years, depending on inflation. Airlines currently pay the equivalent of £10.36 per passenger at Heathrow. The CAA yesterday allowed this figure to rise to 23.5% in real terms to £12.80 per passenger in 2008-2009, while the increase at Gatwick will be 21% to £6.79 per passenger. At Heathrow the charges will rise by no more than 7.5% a year above the retail price index (RPI) inflation for the period from April 2009 to the end of March 2013, while the Gatwick rise will be no more than inflation plus 2% a year.

Despite the fury of its customers, BAA still wasn't happy yesterday. The former state firm, now part of Spanish infrastructure giant Ferrovial, said it needed to put prices up even further to pay for a programme of substantial investment at all its airports, including a fifth terminal at Heathrow to open next week and, it was confirmed yesterday, a second runway at Stansted.

At Scotland's airports landing charges are unregulated. BAA has an even tighter monopoly on the Scottish market, owning the country's three biggest airports; Aberdeen, Edinburgh and Glasgow. It has no plans to raise charges here.

"Our landing charges are now 30% lower than they were 13 years ago," said Donald Morrison, the company's spokesman north of the border.

"We are reducing them at RPI minus 3% every year at Glasgow and Edinburgh and RPI minus 1% at Aberdeen."

BAA's strategy is simple. "Our priority is to get more direct international services," Mr Morrison said.

"There are now about 140 services from Glasgow, Aberdeen and Edinburgh to other international destinations, many forged in the last five years. Domestic traffic from Scottish airports has dipped as more people fly direct.

"But Scotland is never going to have the kind of network of flights that Heathrow has and that's why we must keep our slots there," said one industry insider.

There are concerns. Big airlines readily admit that flights from London to the US are more lucrative than to Aberdeen. But should we worry if we lose Heathrow links?

Danny Alexander, the Lib-Dem MP for the Highland capital, said a decision by bmi to drop Heathrow-Inverness flights earlier this year was a "slap in the face".

A spokesman for Scottish Enterprise said: "Despite the significant increase in direct air routes to and from Scotland in recent years, Heathrow remains an important hub for Scottish business people travelling to meet overseas customers and pursue new markets, and it is therefore imperative that there are regular and reliable services to Heathrow from Scottish airports."

BAA is not the only firm bringing direct flights to Scotland. So too is Infratil, the owners of Prestwick. The Ayrshire hub has been at the forefront of budget flying thanks to Ryanair.

Yesterday it welcomed the First Minister, Alex Salmond, as it revealed the economic impact of its growth. Prestwick, a new report says, generates more than £200m a year for the Scottish economy, including around £173m from inbound visitors. The airport, moreover, supports nearly 3000 jobs. Last year it handled 2.4 million passengers.

The study, by Edinburgh-based SQW Consulting, found that 240,000 passengers would not have come to Scotland if it wasn't for Prestwick.

Prestwick has the capacity to handle some three million passengers, so can it expand further? A masterplan for expanding the airport is due soon, but Ryanair has said it will focus future expansion in Scotland at Edinburgh.

Neil Richardson, Prestwick's spokesman, said dialogue continued with the low-cost giant, but stressed the airport has other clients.

He said: "There are many route opportunities for airlines at Glasgow Prestwick, including new destinations and further services on strong existing routes like London."

Prestwick, however, will have to stretch way beyond its design capacity to carry as many Scottish passengers - or have the same impact on the economy - as Heathrow.

I probably wouldn't fly as often over price'

STEWART PATERSON BUSINESSWOMAN Irene Sime, 51, from Glasgow, is a frequent flyer who has made around 25 domestic and international flights in the last year.

She has flown to Spain to visit her parents, to Italy to see friends, to Los Angeles and France on holiday and to London and Orkney on business trips for her firm, Business Tours Scotland.

She said if there is to be a significant rise in flight costs, it would have a bearing on her decisions on whether to fly or drive and could have an impact on business.

Ms Sime said: "I probably wouldn't fly as often if it became more expensive.

"I would still fly to Spain to see my parents. But taking a flight to Stansted or Luton would be different. I would consider taking the car instead. I already tend to try to avoid Heathrow and Gatwick where possible unless it is for a transfer.

"On the business side of things, it would make me think twice about attending a conference or exhibition if was going to cost a lot more.

"It could also affect whether a client would appoint me if it was going to add to their overall cost."