The company at the centre of a series of anti-fracking protests has condemned "illegal direct actions" against its staff and operations.
Protesters who oppose the controversial process of extracting shale gas blockaded the headquarters of Cuadrilla while others superglued themselves to a PR company used by the energy firm.
The action at Cuadrilla in Lichfield, Staffordshire, and at PR firm Bell Pottinger in central London comes on the first of two days of "mass civil disobedience" which campaigners have pledged to carry out to highlight their stance against fracking.
Activists are currently taking part in a six-day Reclaim The Power action camp in Balcombe, West Sussex, after Cuadrilla began carrying out exploratory oil drilling at the site. Hundreds of campaigners staged noisy protests in Balcombe in the face of a heavy police presence.
In a statement, Cuadrilla said: " Protesters broke into our Lichfield office, harassed our staff and chained themselves to filing cabinets.
"The police are on site dealing with this. We condemn all illegal direct actions against our people and operations."
The firm insisted that the morale of its staff at various sites is "fine", and they and the teams supporting the company are "doing a magnificent job".
"They know that what we are doing is legal, approved and safe, and that shale gas is essential to improve our energy security, heat our homes, and create jobs and growth.
"Cuadrilla is rightly held accountable for complying with multiple planning and environmental permits and conditions, which we have met and will continue to meet.
"Clearly we are held to one set of legally enforceable standards while some protesters believe that they can set out and follow their own."
Campaign group No Dash For Gas said six protesters superglued themselves to the glass door of Bell Pottinger at 8am and deployed reinforced arm tubes to stop anyone else getting inside.
Another activist climbed the High Holborn building and unfurled a banner bearing the words: "Bell Pottinger - fracking liars".
The protest group claims it has obtained a secret recording of a senior public relations officer at the firm admitting that the effect fracking will have on people's energy bills will be "basically insignificant" and said it was playing the recording on a loudspeaker.
Meanwhile, it said 20 protesters shut down the Cuadrilla site in Lichfield by blockading it with their bodies. It said two people inside the building had also hung banners from it saying: "Reclaim the power" and "Power to the people".
A group of around 20 protesters also demonstrated outside the constituency office of Balcombe MP and Cabinet Office minister Francis Maude this morning.
And hundreds of campaigners gathered for a protest in Balcombe, with a group of activists including several disabled people blocking the entrance to the site.
The road was closed, and officers were effectively kettling protesters into a small space in front of the drilling site. At one point police stormed a line of activists with bicycles chained together.
Sussex Police have served a notice under section 14 of the Public Order Act because they believe the crowd of people might cause public disorder, serious damage to property or serious disruption to the life of the community.
At the same time a woman was pulled from the crowd by several officers and put into the back of a police van.
Over a megaphone, a senior officer read the public order notice, asking them to move back so as not to cause an obstruction to Kemp Farm Industrial Park, which is not connected to Cuadrilla or the drilling site.
He said: "A protest or camp across the entrance or on the B2036 road to the south of the Cuadrilla site will not be accepted.
"This will allow a designated emergency services route to the site from the south to be maintained, allowing emergency services to enter if required. It will also allow the access and egress of staff without undue intimidation or deterrence."
Shouts of "shame on you" and "no violence" erupted from the crowd as police tried to move the protesters back to the main gate of the site.
Demonstrators chanted: "We are peaceful, what are you?"
Raymond Obedencio, 43, from Occupy London, said: "It reminds me of the crush on the London Underground.
"I've have been here for the past three weeks to document what's been happening and to document as much as I can."
Vanessa Vine, founder of Frack Free Sussex and Britain and Ireland Frack Free, said people in Balcombe were outraged that there had been no proper consultation about exploratory drilling at the site.
Ms Vine, who lives four miles away in West Hoathly, said: "There have been people who have glued their hands to the gates before but nothing of this scale.
"Yesterday, people all linked hands around the site. They (Cuadrilla) have cynically suspended operations."
She said the police presence was disproportionately heavy and added that Reclaim The Power were "not nasty, violent people" but "altruistic people who are challenging what the Government is doing".
Protest group No Dash for Gas accused police at Balcombe of "an extremely aggressive response" to the demonstration.
They claimed officers charged, shoved and kettled protesters, including disabled people, children and MP Caroline Lucas.
Protester Ewa Jasiewicz, at Balcombe, said: "This is an outrageously aggressive response to a day of principled civil disobedience. All of our actions have safety, dignity and respect at their core.
"Cuadrilla and the Government were desperate to discredit fracking opponents. We offered them no aggression so they are creating it themselves."
Earlier, Sussex Police said on Twitter: "We would like to reiterate that protesters aren't being kettled and are free to leave the site as they wish."
At Cuadrilla's Midlands headquarters, protesters blocking the entrance to the building said the day's actions were only part of a longer-term campaign.
Isobel Tarr, one of group attempting to "disrupt" the company's operations said: "We stand with the people of Balcombe and all other communities threatened by fracking."
She added that Caudrilla and other companies involved in fracking were "threatening a lot of the UK countryside and threatening a sustainable energy future".
Another protester, Lucy Lowit, who was among those blocking the building's entrance, said she was concerned fracking could lead to pollution of underground water supplies.
She said: "It's very dangerous for the water aquifers. They drill a mile down and there's a high risk of water pollution, and once that gets into the system you could be poisoning entire towns and cities."
She added that people were beginning to grow more aware of the issues, and estimated there were more than 1,000 protesters at Balcombe yesterday.
Ms Tarr said public concern had already spread around Europe.
She added: "There are more than 40 community groups throughout the UK and Ireland against fracking in their communities, and several countries in Europe including France and Bulgaria have banned fracking because of popular pressure."
She said: "We intend to disrupt operations of Cuadrilla today to show them that although they've stopped their drilling in Balcombe, we also know they are planning further gas exploration throughout the UK and they will continue drilling in Balcombe unless we stop them.
"So we want them to know we're not going away, we know where they are and we will be following their activities, and making sure our voices are heard for as long as they stay fracking in the UK."