Britain was last night preparing to remember the dead of September 11.

One year on, the nation will come to a virtual standstill for one minute's silence at 1.46pm in memory of those who died in New York, Washington and Pennsylvania.

Security was being stepped up in British cities and at airports for the anniversary which is being marked in London with a national service of remembrance and commemoration at St Paul's Cathedral.

Prince Charles and Prince Harry are due to meet bereaved families of Britain's victims after today's service.

Charles and Harry, who is 18 on Sunday, asked to meet families privately to offer words of consolation.

Prime Minister Tony Blair and other political leaders are also expected to be in the 2,000-strong congregation.

At the St Paul's service, more than 3,000 white rose petals, representing all those who lost their lives, will be released from the Whispering Gallery, inside the cathedral's great dome.

New York policeman Lieutenant Frank Dwyer will mark the start of one minute's silence by lighting a candle at 1.46pm, coinciding with the time of impact of the first hijacked passenger jet on the North Tower of New York's World Trade Centre exactly a year ago.

The impact of the second jet on the south tower will be marked by the lighting of a candle at 2.03pm by leaders of British Jews, Muslims, Hindus and Buddhists.

More than 600 relatives and close friends of the 67 British victims are expected to be at the service, which begins at 1.15pm.

Actress Patricia Hodge will read a poem by T S Eliot and Culture Secretary Tessa Jowell and US Ambassador William Farish will read lessons.

The Bishop of London, Richard Chartres, will address the service, which will be led by St Paul's Canon in Residence Philip Buckler.

"The service is a time to think of those who died but also a time to light a candle of hope for the future," said Canon Buckler.

Square mile will come to a standstill

The Square Mile is expected to come to a standstill as workers in the City recall the horrors of September 11.

The New York atrocities were felt deeply in the City, as workers feared for colleagues, friends and loved ones on the other side of the Atlantic.

The attacks on the heart of the world's financial centre also created panic and chaos on markets across the world.

The London Stock Exchange is stopping for two minutes' silence at 1.46pm, as will the futures and options market Liffe, and most in the City will follow their lead.

Some of the most poignant memorials, however, will be at firms that lost staff in the World Trade Centre.

Shoppers asked to pay their respects

Britain's high streets are expected to come to a silent standstill today.

Thousands of retailers, large and small, will ask shoppers to observe two minutes' silence from 1.46pm.

The British Retail Consortium which represents about 90per cent of retailers has recommended a two-minute tribute.

Spokesman Russell Hamblin-Boone said: ''I can't speak for smaller shops who are not members but I would have thought they would take the lead from the high street and observe the silence."

Stores Tesco, Sainsbury's, Asda, Waitrose, Marks & Spencer, and Woolworths confirmed they would be observing the two-minute tribute in-store.

Marking courage of 343

Britain's firefighters will lead the nation in marking the first anniversary.

Hundreds will gather outside their stations to observe a minute's silence at 1.46pm - the moment the first hijacked plane ploughed into the World Trade Centre - in honour of the 343 New York firefighters who died in the attacks.

Pictures of the heroic firefighters running into the twin towers, rescuing those trapped inside and working tirelessly through the devastation to try to find survivors became one of the enduring images of the tragedies.

Workers across the UK are expected to observe the silence, with offices, factories, shops and at least some television and radio stations falling silent, including BBC1 and ITV. The London Stock Exchange will observe a two-minute silence.