I agree with Brihard, here, that the Parliament will not be extended over this tariff strife.
Many reasons: First, The Emergencies Act and the authority in the constitution for extending Parliament are not related provisions of the law. There are national emergencies that do not fall into the categories of war, invasion (how is that different than war?) or insurrection, which are the only cases permitting the extension of a siting Parliament's term.
Second: One third + 1 of the members of Parliament need vote to refuse the extension for it to not, repeat, not happen. With a HoC of 338 and 120 conservatives right now, there is no way in hell an extension can be adopted by the Commons.