Prof Jacquie McGlade said the UK was shifting away from clean energy as the rest of the world rushed towards it.
She said the cuts in renewables subsidies, coupled with tax breaks for oil and gas, sent a worrying signal to the coming UN climate summit in Paris.
The UK government says it will meet its targets on carbon emissions in the most cost-effective way.
A spokesman said it was "absolutely committed to getting a global deal in Paris".
Prof McGlade said the UK appeared to have abandoned its leadership on climate change, while 150 other nations were making unprecedented pledges to shift towards clean energy.
She told BBC News: "What I'm seeing worldwide is a move very much towards investment in renewable energy. To counterbalance that you see the withdrawal of subsidies and tax breaks for fossil fuels.
"What's disappointing is when we see countries such as the United Kingdom that have really been in the lead in terms of getting their renewable energy up and going - we see subsidies being withdrawn and the fossil fuel industry being enhanced."
Prof McGlade said this was the wrong message to other nations in the run-up to the Paris climate summit next month - and to its preparatory meeting in Bonn this week.
"It's a very serious signal - a very perverse signal that we do not want to create."
It is unusual for a senior UN official to criticise the policies of a leading member state in such forthright terms.
The UK government has promised to reset its energy policies shortly, to explain how it will meet carbon targets while offering fewer subsidies to renewables, following a Â£1.5bn overspend on the notional budget for clean energy.
Ministers say they have to force energy bills down. They want new solar and wind projects to be built without subsidy, although the industry says that is impossible at the moment.
Since the announcements of subsidy cuts in the summer, three solar firms have collapsed, more than 1,000 jobs have been lost in the clean energy industry and energy investors have started to drain away from the UK.
One potential international investor, Paddy Padmanathan, CEO of Saudi-based ACWA Power, told the BBC: "It's been very badly managed because yesterday we had subsidies - today, I'm sorry, nothing.
"That's basically what has happened in the United Kingdom. You [should] phase out the subsidies - work with the industry in a much more measured way."
He said investors would turn away from investing in UK infrastructure as a result.
"They will withdraw, they are withdrawing," he said.
"Everyone is running around the world looking for other places. Thank you very much, I've picked up experience now, the UK is not the best bet, let me go somewhere else. Even the UK companies are looking aggressively elsewhere."
A Department of Energy and Climate Change spokesperson said: "We are absolutely committed to getting a global deal in Paris, which will create a level playing field for businesses, driving innovation and growing the low carbon economy."
The spokesman said subsidies had driven down the cost of renewable energy, leading more people than expected to install technology like solar panels.
"Ensuring subsidies are used where they are needed most, so they can compete with other technologies provides the best value for money for hardworking bill payers," the spokesman added.
Cuts in support for renewable energy in the UK have been criticised by the UN's chief environment scientist.