"Mr Blair, this is a citizen's arrest for a crime against peace, namely your decision to launch an unprovoked war against Iraq. I am inviting you to accompany me to a police station to answer the charge." If you happen to encounter Tony Blair, this is what the multipurpose-campaigner and Guardian columnist George Monbiot encourages you to say by way of introduction. Indeed Monbiot is so keen on this form of address that he has set up a site — ArrestBlair.org — which offers a bounty raised by public subscription, standing at £2,147.54 at the time of writing, to anyone who attempts to use this salutation on Blair. Monbiot has form here, having attempted to "arrest" the Standpoint contributor and former American ambassador to the United Nations and Under-Secretary of State John Bolton for alleged war crimes at the Hay-on-Wye book festival. Helpfully for Bolton, Monbiot announced his plans in advance and was removed from the premises by security. 

Opposition to Blair and the Iraq war is only one narrow front of 50-year-old Monbiot's lifelong campaigning. His first big cause was the fate of native peoples and environmental degradation in the Third World, with angry polemics-cum-travelogues about Brazil, West Papua and East Africa. After this, and turning his emphasis on Britain, he became the media voice of the protest movements of the early 2000s-      anti-corporation, anti-globalisation, anti-roads. As for so many of the protestariat, climate change and what to do about it became the big issue and often the totem pole on which to hang pre-existing demands.

Monbiot's current obsession and the subject of his recent book (Feral, Allen Lane, £20) is "rewilding". He argues that because of over-farming much of the world, and Britain in particular, has become a degraded and diminished place. Nature should be allowed to take its course, moorlands should gradually become forests again, and Britain's uplands should be cleared of the "white plague", otherwise known as sheep. 

Species which once roamed Britain's wilds should be reintroduced —starting with wolves and beavers, previously last found in the 17th and 18th century. Why should elephants (last seen in the UK 115,000 years ago) and rhinos not roam our lands? Monbiot writes, "I have seen no discussion about the reintroduction of elephants to Europe, though I would like to start one."