Some images of the referendum campaign will linger long after September's vote.

Take last week's press conference at the start of Chinese premier Li Keqiang's visit to London. Crocodile smile firmly in place and with a leering glance at a smirking Cameron, Li told reporters he wanted a "strong, prosperous and united United Kingdom".

You'd think Better Together would be somewhat embarrassed at a tyrant's endorsement. But no, Li's comments were described as a boost for the No campaign.

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According to a Better Together spokesperson: "Interventions from world leaders like Premier Li, Pope Francis and President Barack Obama confirm how important the decision we will make in September is. We cannot afford to get this one wrong."

No, not even if it means accepting support from dictators. Well, in the hard-ball diplomatic game played by China, there's no such thing as a free endorsement.

Cameron said the UK's relationship with China is "gaining in strength, depth and understanding." It is, to the tune of the £14 billion worth of trade and investment deals riding on the success of Li's visit.

In China, a Communist Party newspaper told a different story. According to it, the UK is "an old declining empire" with a media "hyping" concerns over human rights in China.

The comrades back home needn't worry. I doubt if this month's 25th anniversary of the crushing of the Tiananmen Square protests came up in Cameron's discussions with Li. Not with £14 billion at stake.

Meanwhile, Miao Deshun completes his 25th year of captivity, his health broken physically and mentally. His crime? Resisting the tanks which killed hundreds, if not thousands, of his fellow protestors at Tiananmen.

In the quid pro quo world of diplomacy, Li's remarks about the Scottish independence campaign was something of a coup for Cameron. It's highly unusual for the Chinese to comment on the internal affairs of another country. It's a key principle for them. We keep our noses out of your affairs in the way we most definitely want you to keep yours out of ours.

So why did Li diverge from his regime's usual practice? Possibly because ideas like 'autonomy', 'independence' and 'referendum' touch a raw nerve in China.

For example, Beijing says Taiwan is part of China. End of story. They'd never entertain the idea of holding a referendum to decide the matter.

Only some days ago, news emerged that the Uighur scholar Ilham Tohti has been jailed after a secret trial accusing him of 'inciting separatism'. Tohti has only ever peacefully advocated greater autonomy for Xinjiang and respect for the rights of its muslim population.

Then there's Tibet. Since they invaded in 1951, it's estimated the Chinese have killed over a million Tibetans. It's a criminal offence to possess a Tibetan flag or an image of the Dalai Lama. Some 99% of Buddhist monasteries have been closed.

A dedicated campaign to wipe Tibet off the face of the earth has been waged mercilessly for over half a century. Even what the Chinese call the 'Tibet Autonomous Region' is barely half of what constituted the historic nation of Tibet.

Despite copious evidence to the contrary, the Chinese assert that Tibet has always been part of China. By destroying Tibetan culture, undermining its language and flooding the country with Chinese migrants, the Beijing government seeks to turn this obnoxious myth into reality. The last thing the Chinese will offer the Tibetans is an independence referendum.

There are lessons in all of this for the SNP. Its leadership has tiptoed around the independence campaigns of nations like Quebec and Catalonia. Two years ago, Alex Salmond turned down the chance to meet the Dalai Lama.

Fat lot of good it has done the Yes campaign. The North American, European and Chinese establishments have all rallied round to support the UK status quo.

The SNP should speak up fearlessly for national self-determination around the world. Like Mr Li spoke up for Better Together.

Miao Deshun, Ilham Tohti and the Dalai Lama need friends who will speak up for them. I doubt Mr Cameron did so during his £14 billion negotiations.