An unprecedented level of security measures has been implemented in Jewish areas by security groups.
Experts stressed that ties with police and politicians were closer than ever, but the Community Security Trust admitted fears among British Jews were "as bad as we can recall" amid concerns of possible copy-cat terror strikes.
CST has requested additional funding from the Home Office and been in regular contact with Security Minister James Brokenshire, who contacted the charity at the height of Friday's attack.
The group said it had received a record number of requests for immediate advice and help since Friday. "Our staff have worked tirelessly to address these and will continue to do so," said communications director Mark Gardner.
"Inquiries have come from a wide range of sources, including parents of schoolchildren, shop owners, communal buildings and the commercial guarding companies that work within our community.
Where we identify security gaps, we will do our utmost to deal with them
"Where we identify security gaps we will do our utmost to deal with them."
One group from a strictly Orthodox Jewish school pulled out of a visit to Golders Green MP Mike Freer at Westminster on Wednesday because of fears about travelling on the tube.
"My constituents are nervous and tense, which is entirely understandable," Mr Freer said. "But if people change their behaviour, the terrorists have won."
CST sent around 10,000 emails advising people on security measures this week alone.
There was an immediate increase in policing in most communities, including special foot-patrols in some areas of London and Manchester.
In north-west London, Barnet's borough commander, Adrian Usher, joined a patrol on Shabbat morning, walking alongside members of CST and the volunteer group, Shomrim, between Hendon and Golders Green.
A surge of volunteers for CST have come forward since the Gaza conflict last summer. More than 150 have completed initial training programmes in the past few months, with others on waiting lists.
Mr Gardner said: "It is a rigorous process because every candidate must provide proper references and then go through an 11-week course that includes both physical self-defence training and security classes.
"The job is a very serious one, so we must train to the highest possible standard. In the past two years approximately 1,500 of our existing volunteers have also undergone a strict refresher programme of retraining."
One communal security expert said everything that was "physically and financially possible" was being done to protect the community. Security has been stepped up at schools and thousands of pieces of security equipment have been installed at synagogues and charity offices in the past seven years. More than 2,000 CCTV cameras, almost 4,000 metres of perimeter fencing and dozens of anti-ram bollards have been put in place.
Shatter-proof film has been fixed to windows in more than 500 Jewish buildings. Such measures have cost more than £5 million since 2008.
Shomrim, the volunteer neighbourhood security group, sent out extra patrols and maintained a higher-than-usual presence last Shabbat. Its newest patrol car, which went into operation last month, was driven by a non-Jewish volunteer throughout Shabbat in Jewish-populated areas.
A spokesman said: "We have had the car out patrolling the entire area of Hendon and Golders Green. We asked the police for extra patrols and the borough commander himself came out.
"Are people running around and hiding? No. There is a level of fear but also an increased security presence and reassurance."
David Cameron met leaders of communal groups in Downing Street on Tuesday and again reassured them about the government's response.
He assured them of an "open-door" for the community to raise its concerns. He took substantial interest in concerns about activity on university campuses.
Among the members of the Jewish delegation attending the annual meeting with Mr Cameron were Jewish Leadership Council chairman Mick Davis, CST chairman Gerald Ronson and Board of Deputies president Vivian Wineman.
As events unfolded in Paris, Home Secretary Theresa May had been at a scheduled meeting with the Campaign Against Antisemitism, the group set up last summer. The session took place hours after she led a Cobra security meeting on the Charlie Hebdo murders.
She is understood to have maintained regular phone contact with CST chief executive David Delew, and in recent weeks has encouraged her key special adviser Nick Timothy to meet other Jewish groups. She chaired Thursday's hour-long meeting with the CAA which included the Director of Public Prosecutions Alison Saunders and College of Policing chief executive Alex Marshall.
CAA chairman Gideon Falter presented a five-point plan for police to tackle antisemitism. Mrs May gave the go-ahead to measures including helping police prosecute anti-Jewish hate crimes and the formal adoption of a definition of antisemitism disguised as anti-Israel political discourse.
