This is the main British military base in the sunbaked desert of southern Iraq. Not so far from here, in Basra city, a Sunni Muslim cleric is shot dead and the Sunni mosques are closed. By the end of May alone an estimated 140 civilians will have been killed. Nine British soldiers will also have lost their lives, making it the army's bloodiest month since the war 'ended' three years ago. The carnage prompts Nuri al-Maliki, the Iraqi Prime Minister, to declare a state of emergency and beg: 'What is going on in this city, the city of martyrs and sacrifices?'

This is a tale of two cities. One is Britain's sprawling Shaibah Logistics Base in Basra province, encircled by 15 miles of wire fencing. But there is a growing gulf between this 'holiday camp', as one officer half-jokingly described it, and the vicious reality of that other city seven miles to the north-east, Basra, where death squads roam and militias fight for power. Once the British soldiers from Shaibah casually drove into Basra in soft hats and open vehicles. Now they venture out only when they have to, by helicopter or in heavily armoured patrols.

For the Iraqis, there is no relief from the daily death toll - yesterday alone, 15 died in a car bomb attack. Some believe the British, mentoring the local army and police, can deliver peace. Others resent what they perceive as an army of occupation that has set up its comfortable home from home on Iraqi soil.

Last week brought the 112th and 113th British deaths since the invasion in 2003. Lieutenant Tom Mildinhall, 26, and Lance Corporal Paul Farrelly, 27, were on a routine patrol when their armoured Land Rover was blasted by a roadside bomb. Mildinhall was on his second tour of duty. 'I didn't want him to go this time,' his mother, Susan, told The Observer. 'I had bad feelings about the whole situation because security has deteriorated so badly, and of course that feeling was borne out. But there was nothing I could do.' The last time Susan and her husband Colin, a retired army officer, heard their son's voice was on the day he died, on the answer machine at their home in south London. 'It was the normal upbeat thing: "Sorry I missed your birthday. Couldn't get to the phone. Lots of love."' The Observer wanted to understand the views of frontline soldiers, so its reporter and photographer embedded with 20 Armoured Brigade at Shaibah, home to most of Britain's 7,200 troops in Iraq.

Saturday afternoon and young British soldiers are sitting cramped in four armoured Land Rovers, dirty, sweaty and swatting at dozens of flies. As the 'snatch' vehicles crawl into the desert, two soldiers rise through each roof, ready their light machine guns and scan the landscape, hoping to suffer nothing worse than the 44C heat.

When this company from the 1st Battalion Devonshire and Dorset Light Infantry was briefed by Lieutenant Mark Whitehouse, the talk was not of 'hearts and minds'. 'There are threats out on the ground: roadside bombs, mortar attacks, hijackings, kidnaps, shootings,' said Whitehouse, 24. 'If we get a contact and a vehicle becomes a casualty, the remaining three bombast out of the way. In the event of smallarms fire, return fire and put down sufficient arms to stop them. We will move to a location where we can capture or kill them.'

Out here the desert is pockmarked with the debris of war. There is dust on our clothes and at the back of our throats. We know that our vehicles are not much defence against the insurgents' improvised explosives. The convoy comes to a halt 13 miles from base, establishing itself as a vehicle checkpoint: Iraqi motorists will have to stop and demonstrate they are not carrying weapons, bomb-making equipment or other suspicious cargo.

The Iraqis they halt in the howling wind do not look amused. Mothers in black abbayas peer nervously from the back seat. Men get out and open their car boots with what looks like bewilderment, fear and humiliation in their eyes. To an outsider, the gap between indigenous population and army of occupation appears unbridgeably wide. Then comes the solution, in theory at least. The Iraqi army arrives and takes over the checkpoint, leaving the British watching, but bored. Earlier the regiment's commander, Lieutenant- Colonel Toffer Beattie, had assured us: 'In our area, the Iraqi army are really rather good. They're proactive, well led, well trained.' The reality on the ground is somewhat different. An officer chuckles, 'If we go away the Iraqis will stop checking vehicles. And if you think they're lazy, the Iraqi police are worse.'

War, or whatever this is, has long banalities between the bangs. At the end of six hours, we return home through the gloom. The Land Rovers must travel with headlamps off to give them cover of darkness, with drivers using night goggles. But a single misjudgment sends one of the vehicles careering off the dirt track and a female captain is taken to hospital with spine and hip injuries. That night at dinner, an officer explains: 'I'd rather drive without lights than draw fire. There is a difference between a risk and a gamble. Risks are calculated. We take risks; the Americans gamble.' The next 'risk' will be a patrol down what he describes as 'RPG [rocket-propelled grenade] Alley' before adding: 'Tomorrow we're going to go out and capture ourselves some Tommy Terrorists.'

But not everyone on our patrol has the heart for much more of this. Lance Corporal Carl Paton, 29, from Torquay, has decided to quit the army after eight years to live with girlfriend Nicola and their five-year-old twin sons, Cyle and Callum. 'I don't want to marry into the army,' he says. 'I'll probably become a postman, something cushy, as I don't mind early mornings. I don't think we get paid enough here. You don't get any "danger pay" or "Iraq pay". You shouldn't get the same as if you were firing blank rounds on Salisbury Plain. We're risking our lives out here.'

The baseat Shaibah, built on an airport, has the incongruous feel of a Little Britain. There is the rigidly stratified army, with the customary echelon of Sandhurst-educated officers. There are the workers from Bangladesh, India, Serbia, Iraq and elsewhere performing menial jobs. There are meals including bacon and eggs, sausage and mash, fish and chips, apple crumble and custard and, of course, curry. There are recreations including a 'fat club' and a website to keep in touch with home. Day-to-day life is relatively comfortable here, in contrast to the mayhem beyond. Major Kevin Shearman, 34, who took part in the invasion, said: 'It's much more dangerous now than it was during the war, but by staying behind the wire you can't go out and do as much as you'd like. We shouldn't be putting guys on the streets to die, but the less we do, the more freedom terrorists have to move around.' When not on duty, the troops can work on their tans under the blazing sun. Smartish cafes have opened and an Iraqi hairdresser and shopkeeper work on site. Unlike in Basra itself, there is a constant supply of electricity, hot running water and air conditioning.

To Blair and Bush's critics, this is what imperialism looks like. Some of the soldiers have done several tours of duty in Iraq. 'Three tours is enough for any grown man,' sighed Captain Iain Mackinnon, 45, quartermaster for the 35 Engineer Regiment Group, and married with daughters aged 16 and 12. Flight commander Dave Abbott, of the Joint Helicopter Force, is on his third tour in 12 months and his fourth overall. In May, after five Britons died in a Lynx helicopter crash in Basra, Abbott, 38, from Ilminster, Somerset, handed in his notice after 20 years. 'I feel very tired,' he said. 'Coming out to Iraq now is like commuting to work. When you come back to the same bed in the same tent it feels like that; the guys leave bits of kit for next time. 'The wife is worried, even more so after the incident with the Lynx. I always said I wanted a second career and Iraq has made up my mind. I'm trying to start a family and spending seven to eight months away is not helping. We're emigrating and I'm joining the New Zealand Air Force.'