What if the opposition is too small to function?!
From the Parlyapp on Xwitter
The official opposition has to shadow each Commons minister (usually 95), provide MPs to sit on select committees and bill committees as well as two Deputy Speakers and members of the panel of chairs (Labour provided 19 in the last parliament). And whips, obviously.
While the number of opposition MPs on committees will reduce if one party wins for example two thirds of the seats, and shadow ministers could cover more than one brief, there is a question whether the official opposition can properly function with fewer than 100 MPs.
150 MPs is a more realistic floor for the official opposition to properly and fully carry out their duties.
HM Official Opposition is the largest political party in the House of Commons that is not in government. Its leader takes the title Leader of the Opposition.