By Matt Maclean BBC News Online

British soldiers are trained to fight in urban environments

But this might not help them overcome the massive difficulties they would face in attempting to control an area like the Iraqi city of Basra.

One factor could be decisive in taking the battle for Iraq to the city streets - troop numbers.

But with thousands of potential defenders in a city like Basra, that could prove a major barrier to coalition hopes of a speedy conclusion to the conflict.

Coalition commanders will be fervently hoping that reports of a popular uprising in Iraq's second city prove true - this could drastically reduce the cost of controlling Basra, in terms of both time and lives.

Charles Heyman, editor of Jane's World Armies, told BBC News Online: "There is a large body of knowledge inside the British Army regarding street fighting. Probably more than any other army.

"Every soldier is trained for house-clearing urban warfare."

URBAN WARFARE Referred to by US as Military Operations in Urban Terrain (MOUT) UK military calls it Fighting in Built-up Areas (FIBUA)

But training alone would not assure success, he warned.

"Basra is a city of over a million people.

"You're going to need very, very large numbers of infantry troops, and you should expect heavy casualties.

"Numerical superiority has got to be at least three to one, and if you really want to crack it, five to one."

Ian Kemp, news editor of Jane's Defence Weekly, said the Army would "clearly" want to avoid street fighting in Basra if possible.

However, he said the composition of the UK's 7th Armoured Brigade - the Desert Rats, positioned near Basra - was "significant".

"A lot of additional infantry have been assigned or are available to them, than would normally be the case," he said.

"The Royal Marines and 16 Air Assault Brigade are equally well trained - the UK does have a lot of infantry in place."

You cannot afford to leave any buildings with potential enemies behind you Ian Kemp, Jane's Defence Weekly

But he added: "If they think the crucial battle with the Republican Guard is going to take place in the next couple of days, it would be best to wait and see what happens.

"But if it looks like dragging on, there's more of an imperative to go in.

"The preferred option of course would be to defeat Iraq then go in as a peace support operation. But they'd still have to clear every house."

If troops did enter Basra, he said, they would have to "clear every single building".

"You cannot afford to leave any buildings with potential enemies behind you.

"First you seal the building off, pour in firepower and then go in, blowing a hole in a wall or going through a window as the door may be booby-trapped.

"Then it's in with grenades and then spray the rooms with fire."

Cold War

Mr Kemp said much of the expertise in urban fighting methods had emerged from the Cold War of the 1980s, when conflict with Soviet-controlled parts of Europe was considered a credible possibility.

"It's something that lots of Nato armies have experience of," he told BBC News Online.

"They were planning for warfare in Germany, where there's a maximum of two kilometres between built-up areas.

"The 80s saw a massive investment in building urban warfare facilities."

UK troop deployment About 45,000 military personnel Majority of troops in Kuwait and southern Iraq Naval task force of 17 ships is in the Gulf 100 RAF aircraft in region Click here for a map of UK troops' locations

The British Army's largest purpose-built facility is at Copehill Down on Salisbury Plain, a mock-up of a small settlement.

This, and similar facilities elsewhere, are known as "skills houses" where troops can practise attacking and defending buildings.

"It's standard training across the Army, especially infantry troops," said Mr Kemp.

"Some units spend more time doing it but all have gone through the training, and will continue to do so periodically."

But, as all soldiers know, training is no substitute for combat experience, and in urban environments this is in short supply.

'Limited experience'

Mr Kemp said British Army experience in Northern Ireland would be of limited use as "it was not a combat operation".

"But it certainly gives soldiers an awareness of urban operations; the need to protect yourself and take advantage of every scrap of cover available.

"Younger soldiers will not have had extensive experience of that, but the NCOs and older officers will be familiar.

"But there's a difference between a policing operation and bringing down buildings."

He said the only recent example of street-by-street urban warfare had been Russian forces in Chechnya.

"Certainly there's no recent experience that any of the American or British armies would have.

"For FIBUA operations you would probably have to go back to the Second World War, when many of the techniques were developed."