You're wrong, as usual, Petra. It's got nothing to do with cheap EU labour. It's because the Tory government is cutting council money and making them think of how they can save by reducing pay for those who applied for the jobs, some years ago, on an annual contract, not an hourly rate.
If they work part time, they are paid pro-rata anyway.
Most TAs I know, daphne, are not admin staff. They are used as supply teachers, and often have to teach whole classes.
Just because other authorities caved in earlier does not make it right.
Anyway, like you say, nothing to do with the EU. Definitely something to do with right wing ideology, though.