Battle stations. The coming election is just the prelude. This month should have seen Britain’s formal withdrawal from the EU, on Boris Johnson’s deal, prior to serious trade talks with Brussels next year. The election should have taken place after, not before, formal withdrawal, to elect a parliament to conduct those negotiations – and with the outcome of those talks then validated by a referendum. That would have been dignified and sensible.

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In theory, that could still happen. The House of Lords could this week delay the election bill – which tears up a constitutional measure, the Fixed-term Parliaments Act, without even bothering to repeal it. If the Lords were not so bloated and gutless, it would delay the bill. In truth, the upper house is not fit for the job.

Up to now, the anti-Johnson majority in the Commons had a golden opportunity to take command of Brexit. Jeremy Corbyn could have used his leverage to force through a soft Brexit. His ineptitude in dealing with the minority parties lost him that chance. He shot himself in the foot. Meanwhile the SNP and Liberal Democrats sensed they would win more votes with Corbyn still at Labour’s helm than if they waited until next spring – even at the risk of putting Johnson and his hard Brexit back in Downing Street. They put party before country. Never has there been a more cynical Commons than this one.

Johnson has not even had to promise – for what that is worth – to “take no deal off the table”. He has merely returned Brexit to square one and concentrated on what he craves: a safe majority. The polls may be unreliable but, with a divided, demoralised opposition, the odds must be on Johnson winning. He will have his unamendable deal passed by January.

That is not the end. Next year comes the real moment of truth: proper negotiations on a long-term trade deal with Brussels. Remember, Britain will still be in a transitional customs union, and it will start to be hit by a tornado of economic bad news. The National Institute of Economic and Social Research says Johnson’s hard Brexit will cost a staggering £70bn or 4% of GDP, the most savage self-inflicted wound since the hundred years war. Johnson has accepted the EU customs union for Northern Ireland. Perhaps he will eventually see that what’s good for Northern Ireland is good for the whole nation.

• Simon Jenkins is a Guardian columnist