To back his assertion, Jenkins cited recent policy U-turns (forestry, NHS, housing) or continued concessions to big-spending lobbies (high-speed rail, Olympics, renewable energy) as examples of how organised groups can manipulate naive and risk-averse coalition ministers.
I agree with this. A well constructed, strategically communicated argument has more chance of progressing under a two-party coalition than it would under a government with a thumping majority. If Margaret Thatcher or Tony Blair did not want to listen, then there was little one could do to change that. The situation is very different now. With two parties in government, whose core philosophies are so diametrically opposed, it is easier to identify and tap into a vein of political support somewhere within the coalition.
However, a major constraint for lobby groups is that the Government has no money to fund new and interesting policy ideas. This was not a problem before 2010 when Labour seemingly put money into every idea it was presented with. Lobbyists now have to be far more creative - proposing policy solutions that do not have price tags attached to them.
Where I differ with Jenkins is his implication that all lobbying is somehow bad; ministers should be their own masters - piloting the direction of policy, able to swat away the irritating special interest groups that are currently so effective at forcing a change of course.
On the contrary, I see 'lobbying' - in the widest sense - as a fundamental right in a democratic society. We would be all the poorer if minister's ploughed on regardless of outside voices. Poll Tax anyone?