The gates are sliding shut. The options are closing. The extremists are refusing to budge, and the centre cannot agree. The only god is time and she is ticking ever louder.

Within the next two days, Theresa May must manoeuvre herself a Commons majority behind a deal that will win another Brexit extension from the EU on Wednesday. That majority deal is now in full view – it would mean the UK leaving the EU with a customs union in place, as agreed with Labour. This would honour the – frankly vague – wish of the 2016 referendum, and it would provide continuity in trade with Europe. It is a palpable compromise, but for either extreme to present it as a national humiliation or catastrophe is absurd. We have been in that customs union without obvious harm for 40 years.

Such a settlement from this week’s Downing Street talks would trigger an EU extension for the necessary clearing up. It might set the stage for a confirmatory referendum, for which there is much to be said, but that is a matter of process and should not be a deal-breaker just now. Keep it simple. Agreement is needed, not reasons for disagreement. A customs union is now critical for hundreds of thousands of people across Britain. Yet zombie MPs wake up each morning and chant cliches like Byzantine theologians disputing the holy spirit.

From the moment May failed to deliver a plausible Brexit without Labour support, a deal with Jeremy Corbyn became essential. It was not to do with his politics any more than with his hat. It was because he had the votes, as had the even less appealing Democratic Unionist party. That is how the Commons works. Also from that moment, May’s own position within her party was at risk. She left it far too late, but two weeks ago she accepted that risk. Her MPs must now show themselves big enough to respect Commons reality – and not tear their party to bits over merely a trade deal.

Corbyn has his own problems, but it is May who is sacrificing her job and her party’s unity to deliver the only Brexit that will get through the Commons. This deal would do what parliament said, over and again, it would do, which is to find a way out of the EU. May can try all the indicative votes she likes, but a customs union looks the only winner. It honours her promise to deliver Brexit. It means the country leaves the EU with minimum disruption. It means May leaves her job with dignity. The nation heaves a sigh of relief.

• Simon Jenkins is a Guardian columnist

• This article was amended on 8 April 2019 to acknowledge that a customs union is not free of friction.