Anyone who has ever tried to organise a party will relate.
You draw up the guest list, carefully selecting the people you want to attend and the people, how shall we put this delicately, who are NFId. Perhaps you had an argument the last time you saw them, perhaps they've been bad mouthing you in public, perhaps they were involved in a high profile court case accusing you of breaking the law in order to rush through cuts to incentives that would devastate the UK's solar industry. Whatever the reason, you don't want them there.
You extend the invitations to your chosen guests. And then one of your most distinguished attendees turns up with a plus one who you had specifically chosen not to invite.
The Sceptic Tank still shudders at the memory of his last Halloween Party, which culminated in Batman wrestling Robin to the ground following a row over whose costume was best. Note to self: Christian Bale is not to be accepted as a plus one at fancy dress parties.
Anyways, it turns out something similar could happen at today's Clean Energy Ministerial (not the fancy dress wrestling part obviously, more the embarrassment that comes when someone arrives who you had secretly hoped would not turn up).
Despite being one of the UK's most prominent clean tech entrepreneurs and a former darling of both the Lib Dems and the Conservatives when they were in opposition, founder and chairman of Solarcentury Jeremy Leggett was none too surprised to find that his invite to the Clean Energy Ministerial had got lost in the post.
After all, he had been heavily involved in the decision by a number of solar firms to successfully sue the government over its illegal handling of cuts to feed-in tariffs, and no one in Whitehall wanted to see this celebration of British clean tech tarnished by a first-hand account of the government's support for one of the world's fastest growing clean tech markets.
But not to worry, because the British government had to invite the US government, and the US government, either being unaware of the little local difficulty in the UK solar market or blessed with a mischievous sense of humour, have invited Mr Leggett to join them the summit.
Jeremy was delighted to accept the invitation and has confirmed that he plans to make the case for continued global investment in solar PV, urge governments to stop pandering to the fossil fuel and nuclear lobby, and best of all call on governments "to resist the temptation to keep undermining successful feed-in tariff policies".
"This industry will continue to cut costs, invest in new products and jobs, but it needs predictable public policy not knee-jerk panic of the type for example that has undermined the UK scheme," he will add.
The Sceptic Tank is sure the British delegation is particularly looking forward to this part of proceedings and like all good hosts will nod along politely, while quietly cursing itself for failing to keep a closer eye on the guest list.
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