This section applies if the trustees of a settlement, while continuing to be resident ... in the United Kingdom, become at any time ("the time concerned") trustees who fall to be regarded for the purposes of any double taxation relief arrangements—
as resident in a territory outside the United Kingdom, and
as not liable in the United Kingdom to tax on gains accruing on disposals of assets ("relevant assets") which constitute settled property of the settlement and fall within descriptions specified in the arrangements.
The trustees shall be deemed for all purposes of this Act—
to have disposed of their relevant assets immediately before the time concerned, and
immediately to have reacquired them,
at their market value at that time.