The government mainly decides if there is a debate if someone actually tries to block the guidance. If the opposition pushes for one it might happen. Obviously the Tories are not going to do that though, but the Lib Dems have a possible opening. This is the process:
Fatal prayer motions
A fatal prayer is a motion seeking to overturn a negative instrument. It will commonly include the wording, ‘That a humble Address be presented to His Majesty, praying that [the instrument] be annulled’. Fatal prayers tabled against a draft negative are often phrased, ‘That the draft instrument be not made’.
A fatal prayer must be tabled within a 40-day objection period, which begins on the day the instrument is laid before Parliament. The objection period is known as praying time. For the prayer to successfully annul an instrument, it must also be agreed by the House within the 40-day period. A fatal prayer has not been successful in the Commons since 1979.
Fatal prayers are not often debated. While the government will typically find time to debate a prayer if it has been signed by a member of the opposition frontbench, it is not obliged to. And on occasions that it does, the instrument may be referred to a delegated legislation committee for consideration, rather than the motion being formally moved in the Commons Chamber. Prayers can also be considered on Opposition Days.
https://commonslibrary.parliament.uk/research-briefings/sn02569/
So what you are most likely to get is an Fatal Prayer - (Early Day motion) against the guidance which MPs can sign to support but has no effect.
However the Lib Dems get three opposition days this session as the third largest party. If one of them falls within the next 40 days they could use one to hear a Prayer against the guidance which could result in a debate and vote.
Will they actual do it? Even if they did the government would win. Having a debate would mean the Lib Dems would face awkward questions about their actual plan and thinking here.
I suspect this maybe just paper opposition they won't follow through. We shall see though.