Internal Conservative research used to road-test different cabinet ministers to decide how to deploy them in the general election campaign found that Boris Johnson was deeply divisive, the Guardian has been told.

A source said the findings, based on research carried out by the company run by Sir Lynton Crosby and Mark Textor, suggested the foreign secretary could have a very negative impact in parts of the country.

As such he was initially more heavily deployed in Tory areas, for example in the south-west, they claimed.

The suggestion was that Johnson – who has previously been seen as a strong election asset by many Tory MPs because of his popularity and success in twice winning the mayoralty in London – had developed a “polarising” effect since the EU referendum.

A lot of anger appeared to be linked to the claim of Vote Leave, for which he was the most high-profile supporter, that Brexit would deliver £350m more to the NHS every week.

The issue was raised during this general election campaign, with one man, Grant Curnow, heckling Johnson during a visit to St Ives by shouting: “You lied to us, Boris. You lied about the money.”

The foreign secretary was also confronted by students carrying protest banners when visiting Balliol College, Oxford, where he studied classics in the 1980s.

Johnson’s potential to be toxic, particularly in strong remain areas, could be a possible setback if he ever took over the leadership of the party – especially given that he used to be one of the very biggest Conservative hitters.

Deborah Mattinson, founding partner at Britain Thinks, said: “Looking at Boris a couple of years ago, in focus groups he was frankly the most popular politician in Britain. It was like he walked on water.

“But the referendum changed that and people saw him in a different light. He is a more divisive figure now. It is a sense that he was in it for himself.”

The source said that the internal Tory focus groups scored Amber Rudd more highly, with some in the party keen on her stepping forward as an alternative leadership candidate to Johnson should Theresa May’s tenure be cut short. Their worry, however, is that the home secretary has a wafer-thin majority of 346 in Hastings and Rye, where she just clung on in the general election.



The Guardian also understands that Rudd could be minded to back the foreign secretary in any future election.



In fact, an MP collecting names for a possible leadership challenger back in 2016 (who ultimately decided not to stand) had marked Rudd’s name down next to that of Johnson. However, she had not declared when Johnson dropped out of the race after being betrayed by Michael Gove, and then offered her wholehearted support to Theresa May.

There is also a suggestion that Rudd may have been one of the five cabinet ministers who contacted Johnson on Friday after the election stripped the Tories of their majority and rumours were rife about a possible leadership challenge.

But a Tory campaign source said there was no move to prevent Johnson from visiting constituencies during the general election, and insisted he was a strong asset to the party. “There were no ‘no-go areas’ for Boris. He was one of our big hitters. This was a Brexit election. The strategy was about appealing to people in Labour heartlands that had voted leave and Boris spoke to that.”

Some northern MPs insisted they considered that Johnson would give them a boost among voters.

A second party source said that while it was true that Johnson was seen as a risk with remain voters, he was viewed as someone who could have an impact and who continued to draw big, positive crowds in strong leave areas, including Labour seats.

However, research by YouGov during the election campaign scoring different cabinet ministers on whether people thought they were doing a good or bad job backed up the findings of the focus groups.

It gave Johnson a +17 score with leave voters, but a -48 with remainers, lower than any comparable score for Rudd, the chancellor Philip Hammond, Brexit secretary David Davis or trade secretary, Liam Fox. Johnson also got a -54 with Labour voters and a -68 with Lib Dems, who are more likely to oppose him on Brexit.

With Conservative voters, YouGov concluded that Johnson scored a more healthy +30 but that was lower than the +55 for Hammond, +41 for Rudd and Fox and +50 for Davis.