In a BBC documentary to mark his 70th birthday, Prince Charles said the idea that as king he would continue making interventions was 'nonsense'. He said he would have to operate ‘within constitutional parameters'. He has campaigned on issues including the environment, wildlife preservation, architecture and the use of GM crops. When asked about what some people call his 'meddling', he said he had always tried to remain 'non-party political'. He said: 'I think it's vital to remember there's only room for one sovereign at a time, not two. So, you can't be the same as the sovereign if you're the Prince of Wales or the heir. The two situations are completely different.' Asked whether his public campaigning would continue, he said: 'No, it won't. I'm not that stupid. I do realise that it is a separate exercise being sovereign. So of course I understand entirely how that should operate.’