Caroline Lucas: The most important politician the Green Party's ever had

The Green Party’s only MP Caroline Lucas has announced that she will not contest the next election. Following the announcement, ITV News Meridian's Political Correspondent Phil Hornby analyses her career.

It was a change in the voting system which allowed Caroline Lucas to become the most important politician the Green Party's ever had.

In 1999, proportional representation in the European elections meant it was easier for smaller parties to win. That's why Nigel Farage and UKIP came to prominence. And it's why Caroline Lucas became the south east's Green MEP.

In the European Parliament she was among friends, joining the Green group which had politicians from across the EU. But when she went to Westminster, as Britain's first Green MP, she was in a group of one.

And ever since, she has ploughed a lonely furrow - but a high-profile one. She's been an assiduous questioner of government ministers, always well-prepared, always ready to ask spiky, direct questions.

It's one of her triumphs, and perhaps her biggest frustration, that the other parties all claim to be green now. There's no doubt the environmental debate has shifted massively in the last two decades - but Caroline Lucas says the other politicians have to go much further, and much faster to save the planet.

When she started out, many mainstream politicians thought the Greens' priorities - the environment, global warming, getting rid of fossil fuels - were a bit cranky. Not many say that now. 

And we haven't heard the last of her. She says her campaigning will go on. And in Brighton, even though Labour won control of the council in May, the Greens will be confident of holding Brighton Pavilion.

At the last election Caroline Lucas had a majority of nearly 20,000. A seat she first won, against the odds in 2010, with a majority of just 1,200, is now one of the safest seats in the south.