INTM483080 | Transfer pricing: operational guidance: working a transfer pricing case: how many years?

It is often practical and efficient in a transfer pricing case to concentrate fact-gathering and discussion on one particular year.

Provided the functions and risks have not changed, and neither have market conditions, then it may be appropriate to extend those conclusions, suitably adapted if necessary, to earlier or later years. Even if conditions were different it still might be possible to apply those conclusions with adjustments to reflect the changed circumstances. Conclusions about the arm’s length price should only ever be extrapolated from one year into other years where it is valid to do so.

Any solution must be defensible at competent authority - see INTM423000.

CH50000 contains guidance about assessing time limits.