At Westminster, Conservative MPs and ministers are warning Theresa May that she must delay Brexit if she cannot secure a deal capable of passing the Commons. But at the Tory grassroots, moves are underway to force the opposite outcome.

The Conservative National Convention – the supreme body of the party's voluntary wing – meets in Oxford tomorrow. Its membership is dominated by the chairmen of constituency parties and its thrice-yearly gatherings are the closest the Tories get to internal democracy. Tests of the collective will of the Conservative membership are very rare.

It's therefore instructive that attempts to get the Convention to reject any extension to Article 50 beyond 23 May are gathering momentum. A motion circulated ahead of tomorrow's meeting by veteran right-wing activists – and passed to the NS – rules out any possible compromise, including the delay suggested by the loyalist Brexit Delivery Group faction today. It is overwhelmingly likely to pass.

The National Convention supports the commitments the Prime Minister has made to the country to honour the European Union Referendum result of 2016 that having triggered Article 50 we will leave the European Union on the 29th March 2019. Another referendum, a delay beyond the European elections, taking 'no deal' off the table or not leaving at all would betray the 2016 People's Vote and damage democracy and our Party for a generation.

Constituency association chairmen have also been urged to remind MPs of their members' preference for a no deal outcome.

It would be very helpful for you to pass on the views of your Association to the Party Chairman and to your Member of Parliament or Parliamentary Candidate. If our Party is to retain the support of Conservative voters and the faith and trust of the electorate in general, then it is vital that we abide by the solemn pledges we made in our 2017 General Election manifesto, in respect of delivering Brexit. We did explicitly make clear that: "No deal is better than a bad deal for the UK" "We will make sure we have (...) control of our own laws" and specifically "As we leave the European Union, we will no longer be members of the Single Market and Customs Union." It is important for Ministers to pay due regard to the Brady amendment passed on 29th January 2019, which mandated the Government to secure wholesale amendment of the Northern Ireland Backstop, in order for the whole Agreement to pass both Houses of Parliament. We encourage senior voluntary party members such as Association Chairmen and Council Leaders to ensure their Members of Parliament make sure that these matters are given priority and that the views of not just Party members, but the wider electorate are not forgotten. We fear the electoral consequences for our party if this does not happen.

Any gesture to either effect by the Convention would be purely symbolic. But it would nonetheless have political force. Significant consequences could yet be felt in parliament. Conservative MPs are more conscious of pressure from their local members than ever before. Several are facing deselection and three of those especially vulnerable to it have already quit. If passed, tomorrow's vote could serve to remind those wavering that their associations are not for turning. One member of the government describes it as a “warning shot”.

Given that we know the fear of a backlash from local members at least in part suppressed the number of Tory MPs who rebelled to back Yvette Cooper's bid to delay Brexit at the first time of asking, a Convention diktat rejecting that very strategy could well have a similar effect ahead of the next set of Brexit votes on Wednesday.