What connects the fears around the government’s EU Withdrawal Bill and John Walker, the retired chemical company worker whose landmark court case has secured the same rights and entitlements for same-sex couples as for heterosexual ones?

The Supreme Court’s verdict that Walker – who paid into his company pension scheme for 30 years but whose spouse would only have received the fruits of payments made after 2005, when civil partnerships were brought in – rested on legal rights enshrined into law not at Westminster, but in Brussels. (Specifically that of “equal treatment” under the law, enshrined in the Charter of Fundamental Rights.)

But as it stands, the government’s Withdrawal Bill makes no provision to recreate those rights and explicitly withdraws the United Kingdom from the Charter. As British law stands today, Walker's husband would, instead of receiving the £45,000 a year that any wife of his would get, instead be given a mere £1,000 a year. In fact, as British law alone stands, Walker's former employers have an explicit right to treat 2005 – when civil partnerships came into force – as a legal line in the sand as far as his rights go.

It is true to say that there is no majority in parliament at present to roll back LGBT rights.

There’s a pretty big “but”, though. Although, at just 66, Walker can expect to live for many more years, no LGBT couple is going to be relaxed about entering a legal no-man's-land, where their rights to pensions and other spousal privileges have no legal backstop while the government “gets around” to legislating to secure rights that will be lost if the Withdrawal Bill as written goes through.

The other big “but” is in the phrase “no majority in parliament at present”. Again, for obvious reasons, few politically-conscious minority groups are going to be wholly reassured by the idea that their rights have no recourse other than the balance of forces in the House of Commons at any given time.

One argument that the opposition parties, and indeed, some Leavers are making, is that as we leave the European Union, there will need to be greater constitutional safeguards created at home to prevent the problem of what Quintin Hogg called the “elective dictatorship”, where any government with a parliamentary majority can rewrite laws and unpick rights at will.

That, broadly, is why the opposition parties will seek to defeat any bill that doesn’t include a cast-iron replacement for the rights ensured by the Charter and the European Court.

Without providing a firm legal guarantee of those rights, either in or before passing the Withdrawal Bill, Theresa May will be unable to secure enough Conservative votes to overcome those objections.