I would have thought that “liable to pay” [ Reg 45(14) For the purposes of this regulation, a taxable relevant trust is a relevant trust in any year in which its trustees are liable to pay any of the following taxes in the United Kingdom in relation to assets or income of the trust—] refers to the tax year in which income and/or CGT etc arises (creating a liability on the part of the trustees) not the tax year when the actual tax payments in respect thereof are due; otherwise, presumably, the wording would have made explicit reference to the tax year of payment or the tax year in which payment was due.
However, it does seem strange Reg 45(14) includes the word “pay”.
Reg 45(3) provides: “The information required under paragraph (2) must be provided on or before—
(a) 31st January 2018;
(b) 31st January after the tax year in which the trustees were first liable to pay any of the taxes referred to in paragraph (14) (“UK taxes”)”.
I don’t think any words are missing although I take the point.
Para (a) applies where for the tax year 2016/17 the trustees have a liability to one or more of the various taxes; trustees having no such liability fall under para (b).