LONDON -- It's not the type of welcome most wedding guests expect before they get into church -- background checks, ID verification and a security sweep.
But then again, Prince William and Kate Middleton's wedding on Friday is no ordinary affair.
Britain hasn't seen a royal wedding of this size since Prince Charles married Diana in 1981 -- there were actually 200 more police on duty for that wedding, which had a longer procession route and a guest list of some 3,500 people, including foreign royals and heads of state.
Friday's wedding will offer much of the same pomp and circumstance with its 1,900 invited guests, but it also presents a modern security nightmare for the 5,000 U.K. police officers on duty. Police will be on the look-out for Irish dissident terrorists, Muslim extremists, anti-monarchists and protesters.
Scotland Yard Police Commander Christine Jones said Wednesday there has been no new terror threat but considerable Internet chatter.
"Our operation has been meticulously planned, and we have thought through and planned for a huge range of contingencies," she said.
Anxious crowds wrapped in Union Jack flags watched late Wednesday afternoon as a convoy of cars arrived at Westminster Abbey. Seconds after, the soon-to-be royal couple arrived at the cathedral for a final wedding rehearsal. Middleton's parents and Prince Harry, the best man, also attended, St. James Palace said.
A wide range of police will be on patrol for as the couple ties the knot Friday: officers on motorcycles, escort specialists, dog handlers, search officers, mounted police, protection officers and firearms units, although only a fraction of Britain's police officers are armed.
Thousands of people are expected along the parade route Friday, a snaking path of less than a mile from Westminster Abbey -- an iconic cathedral near London's Big Ben and Parliament buildings -- to Buckingham Palace, where the new royal couple will appear on the balcony for the anticipated kiss.
Britain has seen several major terror attacks and plots since the Sept. 11 terror attacks in 2001. The deadliest came in 2005, when homegrown terrorists killed 52 commuters during London's rush hour -- Europe's first suicide bombing. In 2006, terrorists in Britain tried to down several trans-Atlantic airliners using liquid explosives. The following year, two major terror plots were thwarted outside a London nightclub and at an airport in Scotland.
London has also seen large protests recently against the Conservative-led government's austerity plans, which aim to cut 310,000 government jobs and raise university tuition fees. Prince Charles and his wife Camilla were shaken up when their car was attacked in December when a student protest turned violent.
A group called Muslims Against Crusades said they wouldn't protest the wedding but urged Muslims to stay away from central London and public transport because of the possibility of an attack. Leader Asad Ullah said the warning was general and not based on any intelligence.
Many Muslims have voiced anger over Britain's involvement in the Iraq war. Prince William's younger brother Harry also served in Afghanistan.
British police have special stop-and-search powers now if they think people in the crowds are carrying something suspicious. Some 60 people have already been banned from the parade route Friday and both uniformed and undercover officers will be in the crowds or on rooftops.
The wedding guests -- kings and queens, sports and entertainment celebrities, charity workers and friends and family of the royals -- will have their identification checked and go through a security screening before entering the abbey. Some of the guests have also gone through cursory background checks.
"They will go through a significant search regime," Commander Jones said.
Although Britain's security threat level remains the same, there has been an increased threat from Irish Republican Army splinter groups opposed to the peace process. A masked man from the Real IRA said Monday the queen was wanted for war crimes and his group would oppose her visit next month.
He made no specific threat to disrupt the royal wedding.
Police said security around London's subway network will be boosted, while policing at Heathrow, Europe's busiest airport, will be as normal.
In October, the U.S. State Department advised Americans to be wary amid reports that terrorists were planning a Mumbai-style attack on a European city. More than 160 people were killed in that 2008 attack, when gunmen fired on crowds in a shooting spree that paralyzed India's business capital for days.
But a U.S. State Department official said the threat expires on Saturday -- the day after the wedding. U.S. travel advisories have set expiration dates unless a threat is still considered active.
"We do not plan to renew it," the U.S. official said suggesting that the Mumbai-style threat was no longer considered active or credible. The official spoke on condition of anonymity because he was not authorized to speak to the press.
Another western intelligence official, who spoke on condition of anonymity because of the sensitivity of his work, said threads of the threat were still being investigated but he added there was "no intelligence to suggest a highly organized threat to the royal wedding."
Forecasters predict a 70 percent chance of rain Friday for London. The Meteorological Office says there will be a mix of showers and dry spells, a cool breeze and temperatures in the high teens Celsius (mid-60s Fahrenheit).
Greg Katz, David Stringer and Toby Goode of the Associated Press contributed to this story.