Theresa May has been warned that she risks losing the next general election if she alienates moderate Conservative voters by pushing through a "hard Brexit".
A group of former Conservative ministers and MPs has urged the Prime Minister not to alienate Conservative voters who backed Remain in the referendum by turning the party into "Ukip-lite".
The intervention comes after the Liberal Democrats overturned a Conservative majority of 23,000 in the Richmond Park by-election with a campaign fought on their demands to avoid a sharp break with the EU.
Writing in The Observer, the former attorney general Dominic Grieve and ex-ministers Alistair Burt and Claire Perry, along with education select committee chairman Neil Carmichael and Bath MP Ben Howlett, said the result must serve as a wake-up call for the party.
"The Conservative Party needs to be alert that there is a moderate core of Conservative voters, who voted Remain, and who want to hear the Conservative government speaking above the noise of the Brexiters," they wrote.
"They do not want the Conservative party to be Ukip-lite, nor to hear that their desire for a negotiated Brexit ... is somehow an attempt to delay or simply an expression of Remoaning.
"They want the Conservative leadership to speak for them, too, and Richmond may be a reminder that their votes have another destination if we don't get this right.
"That moderate voice is crucial for the party to keep the votes of the middle ground who could lose the Conservative party the next election if they take their votes elsewhere."
The MPs also called on Mrs May to set out the broad outline of the Government's negotiating position before she triggers the formal exit process under Article 50.
"As well as making clear that it will pursue its own course, and not be pushed into a corner by those who only advocate a hard Brexit, a government decision to publish its high-level objectives for negotiations would not only bring some certainty into that issue, but also be likely to suggest a tone which would be welcomed by a key group of its supporters," they wrote.
"The vast majority of Conservative voters would unite behind that and the Prime Minister, trusting her to deliver the best Brexit possible."