Gifts received from a mother-in-law are generally not taxable in the UK. This is because the Income Tax Act defines a mother-in-law as a relative. Gifts from relatives are typically exempt from taxation under Section 56(2)(x) of the Income Tax Act, with specific provisos outlining these exceptions.
NO Gift from Mother in law is not taxable since gift received from relative is not taxable as per Income tax act and Mother in law satisfies the definition of relative. For Section reference, you can refer Sec 56(2)(x) of Income tax act (also read Provisio to this section since point related to Not taxable is mentioned in Provisio)