LONDON (Reuters) - Boris Johnson has appointed Dominic Cummings, an architect of Britain’s Brexit campaign, as a senior adviser, a move his team hopes will help deliver the new leader’s “do or die” pledge to leave the European Union by Oct. 31.

The appointment of Cummings, known for a combative style that charms and offends in equal measure, was lauded by some Brexit campaigners who said the 47-year-old provided the only chance of shaking up government to force through Brexit.

But pro-EU lawmakers criticized his return to the corridors of power, with one calling it “an appalling error of judgment”, and noting that Cummings had been found in contempt of parliament earlier this year for failing to answer questions.

Johnson, who will formally become prime minister later on Wednesday, has just 99 days to tackle the Brexit crisis, which has stalled economic growth, brought down Prime Minister Theresa May and left Britain deeply divided.

A source in Johnson’s team confirmed the appointment of Cummings, who worked with the incoming prime minister on Vote Leave, a campaign which was lauded by Brexit campaigners for beating a much better financed campaign to stay in the EU with a simple message that Britain should “take back control”.

He was played by British actor Benedict Cumberbatch in a televised drama, which burnished his credentials as an aggressive campaigner willing to challenge traditional thinking and use data to persuade voters to back Brexit.

Since the 2016 referendum, Cummings, a former aide to Johnson’s rival for prime minister, Michael Gove, has kept a low profile, criticizing May’s Brexit strategy and the actions of some hardline eurosceptics from the sidelines.

“I’m happier about this (appointment) than Boris winning. I’m happier than if I was going into Downing Street,” one veteran Conservative and Brexit supporter said, describing Cummings as a man who “won’t go tame” in the face of pressure from Britain’s civil service of permanent officials.

Many Brexit supporters have accused May’s government of being railroaded by civil servants into adopting a failed strategy on Britain’s departure from the EU and have long hoped for a new leader to change tack - a role now handed to Cummings.

At the time of the referendum, a fellow campaigner said Cummings “uses Soviet propaganda techniques” and ran a focused campaign, sticking to two messages - that leaving the EU would hand 350 million pounds ($437 million) a week to the public health service and that Turkey could join the bloc.

He was found to be in contempt of parliament earlier this year for failing to appear before lawmakers investigating “fake news” and the referendum. He said he had offered to appear and give evidence.

Sarah Wollaston, a former Conservative lawmaker who left the party over Brexit, said before the appointment was confirmed: “If true, (it) would be an appalling error of judgment to appoint someone who has been in contempt of parliament.”

“Very rare for this to happen and would be shameful to be rewarded by PM with such a high profile role.”