Sure. What could a lawyer possibly know about the law?
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In the Telegraph article on school fees (which is dated before the election) Lord Pannick says "It would be strongly arguable that for a new government to impose VAT on independent schools would breach the right to education. That is because all other educational services will remain exempt from VAT and the charging of VAT on independent schools alone is designed to impede private education, and will have that effect." Supposedly Michael Foot and Neil Kinnock were both given similar legal advice in the 1980s and dropped similar policies as a result (although Kinnock says he doesn't recall that).
In the article about housing/compulsory purchase, Tom Barton argues "The ECHR protects the right to peaceful enjoyment of one’s possessions and respect for your right to a home, and capping compensation at ‘existing use value’ could be considered an infringement on this right. Landowners would almost certainly argue that removing or reducing ‘hope value’ in compulsory purchase compensations deprives them of fair market value for their property and infringes their human rights."
The school fees argument seems stronger to me than the housing one and the lawyers making the statements seem to be more eminent but who knows? In either case, even if the government ultimately wins legal challenges could delay things by years, which echoes something I saw Dominic Cummings say about people not understanding how complicated and time-consuming it is for governments to actually do things.
As for the slippery slope point, we're already way down that slippery slope. The ECHR has previously prevented British governments from deporting African rapists because of their right to a family life. I think that's far more significant than stopping either of these policies from being implemented.