If I were the planning minister, Greg Clark, or the housing minister Grant Shapps, I would be terrified. Just as the environment minister, Caroline Spelman, badly misjudged middle England when she thought she could push through privatisation of the English forests without anyone noticing or caring, so these two personable ministers must have imagined that it would be relatively simple to rip up the planning system in favour of enterprise and business.

Wrong. In the past few days, the bushfires lit when they published the draft national planning policy framework (NPPF) in July have spread and they now threaten to join up to rage uncontrolled across middle England. The battle lines for a major political showdown are being drawn up just before the party conferences, and there will inevitably be bloodletting.

In quick succession we've seen a loose coalition of the most powerful and sensible non-government groups expressing deep concerns that the NPPF will lead to a planning free for all and a diminution of local democracy. The National Trust, RSPB, Friends of the Earth, Campaign to Protect Rural England, TCPA, Royal Town Planning Institute, and a host of others such as the Ramblers and Woodland Trust may all have different agendas and priorities, but there is enough common ground for them to now be working together to ditch key parts of the proposed changes.

On Thursday they were joined by 25 of Britain's chief planners. We can expect celebrities, greens, groupings of local authorities, community and voluntary groups, as well as the environmental audit committee and many individual MPs to follow. Sensing which way the wind is blowing, the Daily Telegraph, has quickly launched a campaign to get the proposals changed.

The government appears in disarray, just as with the forests, shocked by the reaction. So far, support for the draft NPPF has only been drummed up from the few property, housing and business groups who stand to gain financially. The Times, for example, splashed on Thursday [paywall] with the outgoing head of the British Chambers of Commerce saying that the government should "hold its course" on the reforms.

The ministers may have roused middle England, but they should be especially scared because they must contend with Dame Fiona Reynolds, the director of the National Trust, who is having one of her Octavia Hill moments and is now emerging as an unofficial leader of this enormous salon de refuses – a kind of French Revolution Marianne figure, a symbol of steadfastness and the common good.

Next week Reynolds will write to all of the trust's 3.8 million members – that is nearly 10% of Britain's eligible voting population – urging them not only to sign a petition against the government's proposed reforms, but to lobby their MPs. At the very least, she expects 100,000 people to sign up.

Cameron and the cabinet – we can assume they are members of the trust – will choke on their cornflakes when the letters arrive. They cannot roll over as they did with the forests because this time huge money is at stake, as well as the government's whole localism agenda.

But I would expect them to announce some major changes, or at least formal peace talks, within a few weeks.