Only KCL claims the 100% employability (for those that went for jobs, I presume they're not counting those that went on to do the full masters or to do something else). But it is fairly well known that there just aren't enough Classics teachers - I went to Manchester for undergrad, one of the largest unis in the country, and I would say that we started beginner's Latin with maybe 50-70 students, and that number had very much declined by the time we were A level standard. Only about 20 people took the Latin course after that.
So I guess not that many people actually have the standard of Latin required, and of those the number wanting to go into teaching Classics will be even lower.