Joe Rukin, of 'Stop HS2', wished to hand an envelope containing a list of complaints to Nusrat Ghani MP, the HS2 Minister, at the event at Dale House Farm.
When she refused, he locked the gates to the farm, which only has one entrance and exit.
Ms Ghani was unable to leave until a locksmith came to cut the padlock off.
Joe said: "Initially when Nusrat Ghani was being told how 'wonderfully green' HS2 was, I presented her with a bow saw to help her clear out ancient woodlands.
"I tried to point out that this was 'greenwashing' and that the reality is HS2 will be incredibly environmentally damaging. I was then escorted off."
But Joe, knowing Dalehouse Farm only had one way in or out, then locked the gates to try and ensure Ms Ghani would get the envelope.
He claimed Ms Ghani was 'having none of it'.
She was at Dalehouse Farm to launch HS2's 'green corridor'. It will use Â£8 million of government funding to create new woodlands and deliver safer roads, according to the government.
She said: "As we deliver the new high speed railway our country needs, driving forward economic growth and better journeys for passengers, it is imperative we set a new standard for protecting and enhancing our diverse woodlands and wildlife.
"HS2’s green corridor is one of the most significant tree-planting and habitat creation projects ever undertaken in this country."
HS2 has claimed the green corridor will include seven million new trees and shrubs along the Birmingham to London route, including oak, silver birch, wild cherry, hornbeam and holly.
It also claims this will result in over nine square kilometres of new native woodlands and habitats for species including bats, badgers and great crested newts.
But The Woodland Trust slammed the plans and said HS2 would devastate the environment.
Luci Ryan, ecologist at the Woodland Trust said: “This is utter greenwash nonsense from an organisation trying to pretend that HS2 isn’t the most environmentally destructive infrastructure project this country has seen in decades.
“Some 98 beautiful, rare, irreplaceable ancient woods will be destroyed or damaged by this scheme. That’s 98 habitats and ecosystems that support a whole host of mammals, birds, invertebrates, fungi and plants.
“And once that ancient woodland is gone, it’s gone forever so while planting new trees is all well and good, it’s no substitute for what will be lost."