A driver was clocked at 100mph in a 30mph zone in Colne on the B1050 by a roadwatch group during lockdown.
The incident was logged on a traffic data device used by the Cambridgeshire Community Roadwatch group on May 16 at 10.43pm.
Just over a week later another driver was clocked doing 75mph on the same stretch on May 25 at 9.52pm.
David McCandless, managing director of the group, said: “The vehicle clocked at 100mph was actually coming out of Colne, ironically in the traffic calming area.
“It has been so much worse during lockdown than before.
“It’s so dangerous because people have been encouraged to go out and exercise yet they risk being overtaken at speed.
“Older people are more at risk because they may misjudge a car’s speed when going to cross the road by just having a glance.”
Campaigners are now urging police to take their findings seriously after residents in surrounding areas say they “fear for their safety”.
“We have video, witness statements and speed guns,” Mr McCandless continued.
“If you report speeding to the police they put you through to the force Speedwatch but these are not currently in operation because of social distancing constraints.
“It’s like the community must fend for themselves.”
Cambridgeshire police has said that their traffic management officer will be investigating the matter.
A spokesperson from the force said: “Our officers routinely conduct speed enforcement patrols across the county to tackle dangerous drivers.
“Speeding is one of the ‘Fatal 4’ causes of collisions and we regularly adapt our response by deploying additional patrols in areas with increased reports of speeding.
“All speed monitoring devices need to be approved by the home office and calibrated to ensure they are accurate.”
Community Roadwatch, which was set up by local residents in 2015, say that their Speed Indicating Devices (SIDS) do in most cases slow drivers down.
In 2017 the group even campaigned for TruCams to be used by PCSOs to address community speeding but had their cause rejected.
The device collects and stores video evidence for speeding and identifies the vehicle make, model and license plate number.
However, their data has seen various traffic calming measures put in place including warnings, give way markings and extended 30mph zones across the district.
To find out more or get in touch with the Community Roadwatch team visit: www.roadwatch.org.uk/cambs/