Board members revealed the trust was "not able to continue" in its current form and faced few options to grow UKT to a “credible and sustainable size” and reduce the 13% discount its shares have traded at for the past 12 months.
They chose the Henderson trust from a range of potential merger candidates and the two investment companies are set to merge later this year.
UKT shareholders will be able to cash in their investment at close to net asset value (NAV), or choose to receive ordinary shares issued by Henderson in the ‘rollover option’.
Any shareholders who don’t make a decision will be automatically rolled onto the Henderson scheme.
David Warr, UKT chairman, said: “Having undertaken a thorough review of the options available to the company, we are pleased to be able to recommend a merger.
“Whilst the board has been satisfied with the investment performance of the company over recent years, we recognise the importance for shareholders of scale and liquidity for their investment and the appeal of an investment in a successor trust that offers an attractive dividend yield and a premium to NAV.
A notice is expected to be sent out to shareholders in May this year, with a general meeting due to take place in June.
Henderson will launch the rollover scheme with an issuance of new ordinary shares in June 2017.
Margaret Littlejohns, Henderson chairman, said: “The board of Henderson High Income Trust is delighted to be supporting this transaction.
“We believe that our long term track record of delivering regular high income and capital growth over time from a portfolio predominantly invested in UK equities will be a compelling rollover opportunity for Threadneedle UK Select shareholders.”