Jeremy Hunt has warned Tories to beware of opposition alliances forming in other seats after pro-EU parties agreed to work together in the Brecon and Radnorshire by-election.
The contest will be an early test for either Mr Hunt or Boris Johnson in Number 10, and could see the Government’s working majority in the Commons fall to just three if the Tories fail to hold the seat.
Chris Davies was sacked by constituents as their MP following a recall petition triggered by his conviction for submitting false expenses claims, but he will fight the seat again for the Tories on August 1.
Both leadership candidates backed Mr Davies despite his conviction – although Mr Johnson mistakenly called him Paul.
With the Liberal Democrats the biggest threat to the Tories, Plaid Cymru has agreed not to field a candidate in an effort to unite the pro-EU vote.
Mr Hunt said similar arrangements between opposition parties were happening in other parts of the UK.
At a hustings in Cardiff, he said: “We have got to be very careful because this isn’t just happening in Brecon and Radnorshire, it’s starting to happen in other parts of the country.
“I have seen elements of that happening in my own constituency.
“That’s why we have got to be a really strong fighting force.”
He said Mr Davies was a “great guy and we have to get him back” in Parliament.
“I’m backing him because he was a great local MP and because I believe that his constituents will also want to back him, the local party backs him, he had a rough time with the administrative error that he made.”
The threat to the Tories meant it was important for the party to unite.
“The last year has not been great for that, but when we unite, Conservatives never can be defeated and we have just got to remember that going forward,” he said.
Asked what defeat would mean, Mr Hunt pointed out “we have a very precarious majority anyway” which highlighted the need for all Tories – and their DUP allies – to unite behind his Brexit plan.
Mr Johnson appeared to muddle up Chris Davies with Paul Davies, the Welsh Tory leader.
He said: “Paul has been selected again … Chris has been selected again, forgive me.”
Once he was clear which Mr Davies he was talking about, Mr Johnson said: “I have a high regard for him and I will go out campaigning for him, of course I will.”
He added: “I will hope very much that Chris wins and I will be campaigning for him. I don’t see why I should automatically budget for his defeat, I think we must fight for every vote in Brecon and Radnorshire.
“If we do sustain a defeat than obviously we still have a majority and we will use that majority to implement our policies.”
Mr Johnson accepted that the party was in trouble following the European elections, “but the hour is darkest before dawn”.
One of the issues likely to feature during the Brecon and Radnorshire campaign is EU funding for Wales and its post-Brexit replacement.
Mr Johnson promised “there will be the full allocation of funds for Wales” – but suggested that a Tory-led Westminster government would play a role in deciding how the money was spent.
“There may be some question about how that money is dispensed, by whom, and we would want to make sure that there was a strong Conservative influence on the expenditure of that £350 million or whatever the sum is,” he said.
Wales receives around £370 million a year of EU structural and investment funds.