The argument that we should keep politics out of sport has always been fatuous.

It is simply not tenable because, by failing to acknowledge the political context to sporting events, the participants and organisers risk tacitly endorsing oppression or human rights abuses.

Sports stars and sporting bodies often wish to steer clear of controversial issues but need to be smart enough to understand that a "three-wise-monkeys" approach must have its limits.

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That does not mean boycotts and bans are necessarily an answer.

The sporting boycott of apartheid-era South Africa was justified and commanded widespread support, with those who breached it frequently vilified. Yet it is hard to measure the contribution it made to bringing about change. Meanwhile a boycott of the Olympic Games in Moscow in 1980 achieved little. It was intended to protest against the Soviet invasion of Afghanistan yet troops remained in the country for a further decade.

Nick Clegg's suggestion that awarding the next football World Cup to Russia in 2018 should be reversed is, likewise, fairly futile.

Instead, the news that the Sri Lankan president Mahinda Rajapaksa will not attend the First World War commemoration service in Glasgow Cathedral provides, paradoxically, further evidence of the value of keeping people in the sporting family.

Mr Rajapaksa's decision to send his high commissioner in his stead demonstrates clearly his discomfort at the international opprobrium his country's actions at the end of the civil war have prompted. The Sri Lankan state is accused of massacring more than 20,000 Tamil rebels in the aftermath of the war and a UN investigation into possible atrocities was launched last month.

Mr Rajapaksa chose not to attend the opening ceremony of the Commonwealth Games, at which the largest of a number of demonstrations was that against Sri Lanka's actions. The reason he gave - that he had never intended to come to Glasgow - was implausible enough, given that he is the Commonwealth Chairman in Office.

Refusing the invitation to the Cathedral service is even less convincing. Heads of government in Glasgow for the Commonwealth Games Closing Ceremony are all attending, but Mr Rajapaksa claims he never intended to fly.

His absence is unimportant. What matters is that Sri Lanka's continuing involvement in the Commonwealth family has helped to highlight the questions about her Government's policies and given a major stage for Mr Rajapaksa's critics.

Sport and politics should not be and, indeed, cannot be completely separated. But Glasgow's Games have demonstrated that the most useful contribution sport can make is to keep errant countries engaged in the global family, build bridges and increase the international pressure for change.

Challenging leaders about their policies, whether through public demonstrations or private diplomacy, is far powerful and can often achieve more than boycotts and withdrawal.