Invesco Perpetual, the UK fund manager, has lost one of its key backers ahead of a crunch vote for control of an investment trust — a battle that is shaping up as a test-case for small investors’ rights just as new fund governance rules are set to sweep the sector.

Invesco has been involved in an increasingly acrimonious row with the independent board of the £120m Invesco Perpetual Enhanced Income Trust since last September, when the trust tried to negotiate down the fee it pays Invesco.