David Cameron has lashed out at Tory Eurosceptics in a sign of the increasing pressure on his authority ahead of a potential Commons showdown next week.

As the fractious issue of Europe threatens to tear the Conservative party apart once again, the Prime Minister denounced what he described as "pessimists" on his own benches.

The Tory leadership could face a tense Commons vote on the European Union as early as next week, following moves by Tory backbenchers to force the issue.

Many Conservative MPs are increasingly unhappy at what they say is their party's complacent response to the shock success of the anti-EU UK Independence Party (Ukip) in last week's English council elections.

Mr Cameron's authority has also come under pressure after a number of senior Tory grandees openly called for the UK to leave the EU.

Yesterday, former cabinet minister Michael Portillo became the latest to throw his weight behind calls to quit. He said he "fervently" hoped the public would have the "guts" to leave the EU.

London Mayor Boris Johnson also entered the fray, backing the Prime Minister's plan to renegotiate Britain's terms of membership, but adding: "We should be prepared to leave if we cannot get what we want."

Both men's comments followed those made by Lord Lawson, the former chancellor who became the first senior Tory to openly call for the UK to exit the EU.

Lord Lawson, Margaret Thatcher's biographer, also revealed the former prime minister was persuaded that the UK should renounce its EU membership after she left office, but had kept her view private.

In a sign of the confidence now felt among Conservative rebels, one went on the radio just 24 hours after regaining the Tory whip to urge Mr Cameron to act. Nadine Dorries had been suspended from her party for six months after she appeared on a TV game show.

Ukip leader Nigel Farage said moves by backbenchers to push a vote on the issue proved that "another storm is brewing" for Mr Cameron.