Theresa May's former deputy policy chief Will Tanner warns that the prime minister and the Conservative party are "sleepwalking into opposition."

Tanner, who is now Director of the new Conservative think tank Onward, spoke to Business Insider in an exclusive interview.

Tanner described the move of ethnic minority voters away from the Conservatives in 2017 as "painful" and suggested that attempts to win over younger voters had been "patronising."

LONDON – Theresa May and the Conservative party are "sleepwalking into opposition,"a former senior aide to the prime minister has told Business Insider.

Will Tanner, who was Deputy Head of the Policy Unit at Number 10 until he resigned in the aftermath of May's failed 2017 general election campaign, said the party had failed to stop young and ethnic minority voters from deserting the party.

Tanner, who is now the director of Onward, a new Conservative-aligned think tank, said that May had failed to find a new direction for the party and now risked the "terrifying" prospect of a government led by Labour leader Jeremy Corbyn.

"The energizing zeal of pre-2010 policy or that of the first months under Theresa May [is] not there anymore, and we're sleepwalking towards opposition. The prospect of a hard-left government is terrifying, it would be a tragic end to what could've... could still be a reforming government".

He added: "After eight or nine months out of politics I was depressed by the lack of zeal and energy. Centre-right thinkers had run out of steam."

The Conservatives have failed to win over BAME voters

Ruth Davidson, Will Tanner and Margot James Onward

Tanner also bemoaned the party's failure to win over ethnic minority voters with the party overseeing a 6% swing to Labour in the general election.

With BAME voters also turning out in greater numbers, some analysts believe it cost the Conservatives even more than previously, with the Telegraph reporting it could be the reason May failed to secure a majority.

Tanner labelled the 2017 slide back "painful", saying that the party needed to do much more to demonstrate "that the Conservative Party gets it and is on their side".

He said that while a greater representation of ethnic minority politicians in the party would be welcome, it was more important to recover efforts begun under former prime minister David Cameron to convince BAME voters on policy.

"It doesn't matter where you're from, you can still have the relationship with those communities...Cameron did it well as PM, and May did it too as Home Secretary with Afro-Carribean communities over stop and search and mental health," he said.

Attempts to win over millennials have been "patronizing"

Will Tanner, Director of Onward Onward

Tanner also spoke out about the "patronizing" attempts to win over younger voters by senior Conservative politicians.

"There are a lot of assumptions about millennials [being] individualistic, I don’t believe that to be true, and not true in aggregate either," he said.

"Non-political Millennials value community and the NHS, not necessarily in favour of lower taxes, but are aspirational and enterprising... It’s patronising and ill-thought through to generalise."

Onward are set to launch a major polling and focus group research project looking at the policy preferences of young people.

The research is set to include how young people perceive political parties and how they can be attracted to centre right ideas.

Tanner said that he wants to "challenge the widely held assumptions and identify the reasons they don't vote Conservative, and what attracts those that do to the centre right."