'I found myself getting wound up about what was going on in the world and wanting to do something about it in some way,' he explains, in his gentle - if slightly intense - manner.
With Amnesty leading calls for scrapping the Anti-Terrorism Bill, Blakemore admits his decision to leave the BBC, where he spent eight years, was a huge leap. 'It was a wrench. The BBC makes you feel closeted and well looked after,' he says. Yet his tendency to get 'fired up' and attempt to 'change the world' was restrained at the Beeb; he believes his biggest accomplishment there was kick-starting the careers of work experience protegees.
At Amnesty, where he has been responsible for relations with the British media since last autumn, he says his biggest achievement thus far is generating enough publicity to get a stay of execution for two Iranian women. They were facing imminent death for 'crimes of morality' until Amnesty drew the attention of the world's media to their plight just before Christmas.
Yet Blakemore, who has an optimistic, almost zealous, approach to Amnesty's work, says: 'The downside of doing something worthwhile is that you always feel you want to do more.
'I'd never feel comfortable completely selling my soul and doing PR for a product or service I didn't think was very good.' He pauses. 'I risk coming out as sounding terribly pious,' he laughs.
'Very principled' is how his former boss, BBC director of comms Jennie Allen, describes him: 'Despite his quiet demeanour, Mike has a black and anarchic sense of humour - and he's very good at making fun of himself.'
Blakemore comes across as genuinely modest, repeatedly attributing most of his career success to luck: 'I've been very fortunate. All the jobs I've had in PR have been in things I've been interested in, things I've been able to believe in. That's very important to me.'
It was for this reason that he forsook journalism, originally his 'dream job'. Turned off by the 'worst excesses and sleaze' of 1980s tabloid journalism while working in a regional press agency, he says he fell into PR when a job came up at his local hospital. There he helped save someone's life, this time via a media campaign for a liver transplant donor.
Ironically, given his misgivings about tabloid journalism, it is in the tabloids and mid-market newspapers that he wants to target for Amnesty: 'There are certain newspapers that are receptive to Amnesty's message, but we don't want to preach to the converted. We want to reach people who we can engage with in debate.'
Broadening the range of the charity's target media is a priority for Blakemore, and he is especially keen to drum up more support from teens, students, ethnic minorities and trade unions.
His experience in consumer PR at BBC Magazines proved particularly useful during the NGO's latest attempt to reduce domestic violence in the UK, part of its 'Stop Violence Against Women' initiative. Blakemore led a PR campaign around a series of disturbing ads for a fake cream, Cachez, which could 'finally' cover up bruises.
Cachez, he says, is just one example of how much emphasis the NGO places on media relations and its integration within a wider marketing strategy - it set out to gain coverage in the tabloids to reach younger men.
He is full of praise for his seven-strong team, who he says have got a real belief in what they are doing, and is very proud of Amnesty's new ultra-modern building in Hoxton, which allows volunteers public access to its resources.
But what comes across most is Blakemore's strength in his personal convictions.
On the Anti-Terrorism Bill, his argument is all the more persuasive for its simplicity: 'It can never be right that people don't know what they're being accused of, or they don't have a chance to answer those (allegations).'
As Allen says, he is a 'man of huge integrity', with the communication capabilities to match.
1984 Trainee reporter, Dover & Deal Express
1987 Reporter, INS News Agency
1988 Press officer, North Thames Regional Health Authority
1995 Press & PR manager, BBC South East
1996 Programme publicist - channels, BBC Worldwide
1999 Head of press and PR, BBC Magazines
2004 Media director, Amnesty International UK