Following by-election defeats in Tiverton and Honiton and Wakefield, the treasurer of the backbench 1922 Committee of Conservative MPs, Sir Geoffrey Clifton-Brown, has suggested his colleagues have  “difficult decisions” to make around the prime minister’s future.

The comments by the veteran MP, follow the surprise resignation of the Conservative Party Chairman, Oliver Dowden MP.

In a carefully worded 6am resignation letter, one that was likely drafted before the by-election defeats, Mr Dowden wrote, “We cannot carry on with business as usual. Somebody must take responsibility and I have concluded that, in these circumstances, it would not be right for me to remain in office”.

Mr Dowden is the first Cabinet minister to resign since the ‘partygate’ affair. In a resignation letter, whose significance may lie in what it does not say, the former Cabinet minister fails to offer any endorsement of the prime minister.

In 1990, shortly after her own no confidence vote victory, the wider Cabinet turned against then prime minister, Margaret Thatcher, when she was away at a foreign summit in Paris. With Mr Johnson now out of the country for 8 days, and in light of Mr Dowden’s resignation, the private discussions of Cabinet colleagues do pose an immediate moment of risk for Mr Johnson.

Thereafter, the public reaction to the Conservative electoral defeats by Sir Geoffrey Clifton-Brown MP provides further cause for concern for the prime minister.  Sir Geoffrey’s latest intervention suggests Mr Johnson’s opponents are far from willing to draw a line in the sand after the prime minister’s recent no-confidence vote victory.

In normal circumstances, having previously won a vote amongst their colleagues, a Conservative party leader can expect to avoid a fresh leadership challenge for 12 months.

However, the rules around a ‘no confidence’ challenge are not published in the public domain, and it is understood that this part of the Conservative leadership election process can be changed at any time by the executive of the 1922 committee in consultation with the Conservative party board.

The executive of the 1922 committee is dominated by MPs who appear hostile to the prime minister, including William Wragg, Nus Ghani, Gary Sambrook, and Sir Geoffrey-Clifton Brown himself.

Speaking on the BBC Radio 4 ‘Today’ programme on Friday, Sir Geoffrey responded to the suggestion that his committee may change the rules that protect Boris Johnson from a further leadership challenge, by saying, “I am not going to speculate on behalf of my colleagues on whether we should or shouldn’t change the rules”.

However, as he continued, the Conservative grandee appeared to be doing very much that….

He said: “What is going to happen in the next few days is that the prime minister is going to set out, to both his cabinet and to us as members of parliament, his response to the problems we face in this country”.

“We in the parliamentary party will then have to make a judgement as to whether we think that is a satisfactory explanation or whether we should actually take steps to have a new prime minister.  But I am not going to speculate as to how that process will turn out”.

“I have got an AGM tonight, I will consider what my members say, I will then discuss this matter widely with my colleagues. We will hear what the prime minister says, and then we will have to make some difficult decisions, no doubt”.

Earlier in June, Boris Johnson won a no confidence vote by 211 votes to 148. Should a future contest be facilitated by the executive of the 1922 Committee, some 32 MPs would need to change their previous allegiance to oust the prime minister.

With Johnson thought highly unlikely to fall on his sword, and with the Cabinet (as of now) appearing loyal to the prime minister, the approach of Sir Geoffrey’s executive committee to a future no-confidence vote has undoubted significance.

Following the two by-election losses on Thursday night, the former Conservative Party leader, Michael Howard, became the latest figure to call on Mr Johnson to resign.