Just one fifth of people think Theresa May is actually going to get the Brexit deal she set out in a major speech this week, a new poll shows.

The YouGov research reveals most believe her goals would be good for Britain, but a majority suspect she will not achieve them.

European diplomats have raised questions over the feasibility of Ms May concluding both withdrawal talks and a new trade deal with in the two-year time scale set out in regulations, while Ms May’s own MPs have raised questions over how much of her agenda she can achieve.

Asked whether they thought the European Union would agree to the sort of deal Ms May set out on Tuesday, just 20 per cent agreed to some extent, while 56 per cent disagreed.

One Tory MP told The Independent: “She’s analysed what people were talking about they wanted during the referendum and promised it to them. So yes it’s popular, yes there’s a danger of pandering to the hard right in that, but generally most people will now think ‘great, let her go away and get it’.

“But the British people have a heavy dose of cynicism when they are confronted by politicians promising things, so of course they are not convinced.

“It also raises a question of how sympathetic they will be if she comes back when a recession happens, or when negotiations go normally and she fails to achieve things, and says ‘sorry, this isn’t possible anymore’.”

Others pointed out that the high approval ratings were off the back of a speech which still left many questions unanswered about how she could achieve her aims.

Theresa May calls Brexit a 'great moment of national change'

Labour MP Emma Reynolds said: “One of the gaps is this customs union question, it’s not clear if what she has set out is legally possible.

“She does need to give more on where that is going to leave manufacturers in the automotive or aerospace industries that are worried about delays at the border.”

She added: “I was also concerned that they thought they could negotiate the Article 50 [withdrawal] part, and the Free Trade Deal all at the same time.”

Putting the question of feasibility aside, Ms May’s plan was well received, with 55 per cent believing it would be good for the UK and 53 per cent saying they would be happy if she got what was she was asking for.