A Metropolitan Police spokesman said: "We are not prepared to discuss matters of security."

The details of Miss Middleton's wedding gown have also been a tightly-held secret, with the names of a number of designers being put forward by royal-watchers from Amanda Wakeley and Jenny Packham to Oscar De La Renta, Giles Deacon and Alexander McQueen.

Reverend Nick Wynne-Jones, who is the church's resident priest, is expected to officiate at the wedding.

A woman who answered his phone on Friday said he would not be able to talk about it because he had "signed a no comment contract".

As an Anglican church, St Mark's must open its doors to parishioners as weddings are deemed to be public events under Church of England guidelines.

The legal advisory commission of the General Synod published its guidance on celebrity marriages in April this year, when it said: "A marriage is a public ceremony which at the least all parishioners (including those whose names are on the electoral roll) are entitled to attend."

This was regardless of whether those who lived in the parish were Anglican or not, it added.

Ian Southall, manager of the Englefield Social Club on the Englefield Estate, said the village had been busy with people making arrangements for the big day, many of whom included the world's media.

The feedback I'm getting is just, it's happening. Apart from all the extra traffic it's not going to affect me personally. I think a few people will go up (to the service). I saw lots of people around the church, I presume a lot of people were press.

He added he did not think the wedding party would be dropping in for a dram of whisky from the club's stock of single malts.

They are not coming into the club, the club is getting used for something but I cannot really comment We've been asked not to speak to the press, I don't know why because we don't know anything.

With the Middleton family home just a few miles away in the village of Bucklebury, the couple and their guests will not have far to travel for the reception, which is reportedly being staged in the grounds of the property.

Deliveries of equipment and goods have also been seen going into the substantial house, with reports claiming the family have spent tens of thousands of pounds on a glass marquee and upmarket portable toilets for guests.