Seagull attacks are on the increase as Bristol's population now exceeds 2,000 breeding pairs – costing taxpayers at least £30,000 a year.

Currently at the height of their breeding season, the city's gulls are more aggressive than ever and a leading expert says the troublesome birds are "spiralling out of control".

Bristol City Council already spends £30,000 each year trying to combat the problem by oiling gull eggs so they do not hatch.

But Phil Luker, the pest bird development manager for Rentokil, believes the true cost to the city could be in excess of £100,000.

Over the past five years, the population has increased by up to 15 per cent. Mr Luker spends his life in a constant battle against the ever-growing numbers of urban gulls.

He spends much of his time in Bristol, where he says the number of reported cases of gull aggression against people is alarmingly on the rise.

He said: "The bird starts off with warning calls to try to keep you away from their young.

"If this fails, the gull makes a low pass within a metre or two of your head. Gulls are colony creatures, so they will also give out an alarm call, which will drive all the other gulls in the area to join in the attack."

As if on cue, the skies above Phil's head start teeming with a cross- species confederation of herring gulls and black-backed gulls, all of which are circling threateningly.

"If we were to stay here much longer, the next stage of the attack would be for the birds to defecate and vomit on us. They use their bodily functions as a bombing system.

"And if this doesn't encourage you to get out of the way, that's when they would attack – swooping at you from behind, and raking your head with a special attack claw on their heel.

"The sharpness of the claw, and the impact of a 1kg bird striking at 40mph, means the wounds can be severe."

Phil added: "We have statisticians and gull experts working on a figure for what it costs the city, but it has to be in excess of £100,000 each year.

"That's not just in terms of the pest control measures put in place by businesses and the council, but it's looking at the wider issue of lost custom that businesses suffer as a result of the birds' aggression.

"If a restaurant has birds swooping over outdoor tables, it can stop customers coming back, and if you're woken up at dawn by a calling gull outside your hotel window, there's a good chance you won't return to that hotel again."

Bristol's rich mix of architecture, ranging from Norman churches to Georgian squares, provides one of the biggest attractions of the city.

However Phil says the characteristics of these buildings make them more susceptible than most.

He said: "Features such as over-hanging parapet walls and embellished cornices provide attractive nesting spots for gulls, and the build-up of acidic droppings and nesting materials that they bring with them can cause significant damage.

"As many of Bristol's buildings are Grade I or Grade-II listed, options for removing birds are more limited than usual, and so early preventative measures are a better option."

But it's not just old buildings that can be problematic.

He added: "Modern office buildings often have high roofs and straight sides – not dissimilar to the sort of cliffs where gulls nest in the wild.Life is easy for gulls in our cities.

They would never go out to the Bristol Channel to catch fish. There's more food than they could ever need on our landfill sites and littering the city.

"Most of the bones you find around gulls' nests are chicken bones. They're living on the remains of discarded buckets of fast food chicken legs.

"Combine this with the fact that they hardly have any real predators in the city – only the occasional hawk or falcon – and you have all the right ingredients for a boom in gulls. The population of these birds looks look set to spiral out of control.

"As a pest control company, we use a variety of methods to try to deal with the issue. If the birds are not settled on a building, we can prevent them arriving by installing spikes, high frequency sound systems, nets or charged cables that work like electric fences to give the birds a harmless shock.

"The council runs a system of replacing the birds' eggs with false ones. This works better than the old method of oiling the eggs with paraffin to suffocate the embryo inside, because as soon as the oiled egg starts to decompose, the mother bird will simply lay another.

"But there are only so many false eggs that the council can afford to get out there, and it takes three years before you see any results – which is how long it takes for the chicks to mature enough to return to their place of birth to breed themselves.

"Gulls can live for 35 years, and in urban environments they are able to breed three times a season, so they are very difficult to control without resorting to a full-scale cull, which would need to be initiated by the Government on a national level."

Phil believes the best way to tackle the problem is to eradicate their food sources and their nesting sites.

"It's simple things like encouraging people to keep the lids down on their bins," he said. "There are still lots of people putting black bags outside their wheelie bins. A gull can get into a black bag without thinking twice.

"Another important way forward would be for architects to speak to us during the planning process, so we can advise them on ways to reduce the number of attractive nesting sites in their new buildings.

"Sometimes it only takes the slightest adjustment – like increasing the angle of a ledge – to prevent the birds from getting a foothold on the building.

"For example, I walk past the new Cabot Circus development with my head in my hands, because it has been built in such a way that it is an ideal nesting site for gulls," he added.

The shopping centre has already been forced to employ falconer Rob Rowe to fly a harris hawk near the £5-million domed roof once a fortnight to prevent gulls from spoiling it.

A special kite, designed to look like a falcon, has also been attached to the roof to frighten off gulls.

"There is never going to be an easy solution," Phil says. "Butin Bristol, it's a battle the gulls are winning.

"It's a sensitive subject, because they're such beautiful birds. People can become very emotional about it. The last thing we would ever want to do is to actually kill birds.