The move is the latest in a number of campaigns centred on the park since the bypass was given the go-ahead by the Scottish Executive in the summer.

Four men and a women have been at the camp, in trees at the north-west of the park, since last Tuesday in a bid to stop them being chopped down. The trees are due to be felled before March to start off the £40 million plan.

This is the case because, under environmental laws, this must be done before bats, who inhabit the trees in the spring and summer, return from hibernation.

Liz Robertson, spokesman for the Save Dalkeith Park campaign group (SDKP), understands why the protesters feel they had to take the action but said that they are not part of the official campaign.

"We have tried every other possible means of campaigning and nothing has happened so we can see why the group feel they have to protest in this way. We have no objection to it," she said.

Midlothian Green Party also gave their backing to the eco-warriors and Lothians MSP Mark Ballard was set to visit them earlier this week.

Convener Ian Baxter explained: "When our elected representatives pay scant regard to the views of anyone but the road lobby it is hardly surprising when people who care about the environment start to take matters into their own hands.

"Midlothian Council can diffuse this situation easily by setting up a public inquiry to address all the issues and I call on the council to do so immediately."

A spokesman for the Executive said this week that no work would be carried out to remove the trees if bats were present and if that was the case "work will be halted until a licensed bat surveyor can attend".