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.
Police will be on the lookout for Irish dissident terrorists, Muslim extremists, anti-monarchists and protesters.
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 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.
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," Scotland Yard Police Commander Christine Jones said.
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 Saturday -- the day after the wedding.
"We do not plan to renew it," a U.S. official said, suggesting the Mumbai-style threat was no longer considered active or credible.
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 mid-60s.