Bailiffs and police took over the Lewes Road community garden in Brighton at 2am today.
They fenced off the former Esso petrol station site which is due to become a Tesco store.
The overnight action comes a day before Caroline Lucas, the Green MP for Brighton Pavilion, was due to meet Tesco representatives in London.
It also comes a day before landowner Alburn Retail, also known as Alburn Minos, was due to sue two campaigners for thousands of pounds in legal costs.
The company’s claim is against two members of the Say No to Tesco on Lewes Road campaign group.
Campaigners initially turned the derelict petrol station into a community garden in May last year as the site had become an eyesore.
When it became known that Tesco wanted to open a store there, the community garden became the focus of a campaign to keep the company out.
The campaign group’s Facebook page has more than 2,700 members and Tesco has been in contact with the Green councillors for the ward.
The leaders of the campaign group and their “guerrilla gardeners” were due to leave the site on Monday 28 June this year.
After the overnight takeover of the plot, on the corner of Edinburgh Road and Lewes Road, Mr Blinkhorn said: “A fence has gone up and diggers are on the site.”
He and Ron Edwards were due to appear at Brighton County Court tomorrow but Mr Blinkhorn said that they wanted the hearing delayed to enable them to seek legal advice.
Mr Blinkhorn said: “I’m putting together a series of witness statements.”
One campaigner said that the bailiffs claimed to have a High Court order but would not show it to any of the residents who turned up as the site was taken over.
Sussex Police said that their presence was solely to ensure that there was no breach of the peace.
The site is due to be turned into two shops and seven flats.
