South Yorkshire chief constable Meredydd Hughes said officers were searching the internet for information about protesters seeking to disrupt Pope Benedict XVI's four-day stay.
Hundreds of thousands of people are expected at gatherings in Glasgow, London and Birmingham next month for the first Papal visit to the UK since 1982.
The events are also likely to attract demonstrations from campaigners on issues including gay rights, abortion and child abuse by Catholic clerics.
Mr Hughes, the Association of Chief Police Officers' co-ordinator for the tour, will join the Pope on his travels across the country while officers in London study intelligence and liaise with protest groups.
In particular, police will focus on any "fixated individuals" who might pose a risk to the Pontiff's safety.
Mr Hughes is not in charge of the policing operation – a responsibility which lies with the chief constable of each area the Pope visits – but he is overseeing how police forces liaise with Government departments and the Vatican.
He told Police Review magazine he had agreed a policy with the Metropolitan, Strathclyde and West Midlands police forces that protests will be allowed close to civic events but not at religious ceremonies.
"It will mean that people can express their feelings about the Pope at civil events but will ensure that religious ceremonies, which are very important to the people attending, are not disturbed," he said.
The Pope's tour is due to begin in Edinburgh on September 16 when he will meet the Queen.
Later that day, he is due in Glasgow where he will celebrate mass and hear Pop Idol winner Michelle McManus sing.
The next day he will be in London to see Catholic students at St Mary's University College and to meet leaders of other faiths, including the Archbishop of Canterbury.
All four living former Prime Ministers – Margaret Thatcher, John Major, Tony Blair and Gordon Brown – have been invited to hear the Pope address civic leaders at Westminster Hall.
The Pontiff will remain in the capital on September 18 to meet David Cameron, Nick Clegg and Harriet Harman.
He will then celebrate mass at Westminster Cathedral before taking part in a prayer vigil in Hyde Park for the beatification of Cardinal John Henry Newman, a 19th-century theologian who converted from Anglicanism to Catholicism.
The Pope is due in Birmingham the next day for Cardinal Newman's beatification mass, which will bring the theologian a step closer to becoming England's first non-martyred saint since the Reformation.
As many as 250,000 tickets have been distributed but police expect thousands more people to arrive.
Mr Hughes said: "Our fear is not for those who are turning up with tickets who are coming into a very well organised event but for those who will turn up 'on spec'.
"The lure of the Pope for the Catholic population is so great that we believe many will turn up even though they do not have tickets. We need to ensure that they are kept safe as well, so we are doing a lot of work with the organisers to make sure there are appropriate arrangements in place for them."
The policing operation will involve 5,000 officers in England and 3,000 in Scotland. Mr Hughes said the experience would be "unique" for many of them.
"The breadth of the people coming in age, infirmity and religious fervour means this is a very different event from the football crowd. This is about a wide variety of people coming together in celebration of a very special event that happens at best every 30 years or so."
UK TAXPAYERS FACE HEFTY SECURITY BILL
The tight security measures surrounding Pope Benedict XVI will leave UK taxpayers with a hefty bill.
Even before policing operations are added up, the Papal visit is expected to cost as much as 12m.
Catholics have been asked to contribute towards the cost of the first visit to the UK by a Pope for 28 years.
About 80,000 people are expected to the Hyde Park vigil alone, for which security costs are likely to exceed 1.8m.
A Cabinet Office spokesman said: "Non-policing costs of the visit incurred by the State are expected to be in the region of 10m to 12m. We expect policing costs to be paid for by the State from existing police budgets."