the legal requirement on education authorities to provide free transport to schools has been there since (if i remember right) the 1944 education act - kid needs to live more than 2 miles away (under 8) / 3 miles away (over 8) and it needs to be nearest / designated / catchment school - the law that expanded parental choice didn't expand the right to free transport.
and where a pupil has special needs / disabilities, then it's based on the nearest appropriate school, and the distance is not relevant if their needs / disabilities mean they couldn't be expected to walk there.
this is nothing at all new.
and yes - education authorities will use whatever combination of taxis, minibuses, coaches, buses works best / is most cost effective. if you have got 50 kids travelling from the same area to a secondary school, a coach / single deck bus makes sense. if you've got 50 kids travelling from all round a big rural county to a special school, it probably doesn't.
i've been out of the game of directly organising school transport for some time now - it requires some transport skills and a lot that are more a welfare officer / social worker. some councils' education departments maybe don't have quite enough of the former.
whether more children with SEND should be accommodated with reasonable adjustments in mainstream schools, and whether there are enough schools (mainstream or not) that can accommodate SEND kids near enough to where they live are valid questions, of course.
and hmm at transport across the fen and heath. i have a feeling i may have been one of the people organising school transport in that patch in the 90s (i started there in 1992 so our paths may not have crossed directly but it's possible i may have been and checked your ticket once...)