For the more than 300,000 investors trapped in Neil Woodford’s defunct flagship fund, the UK regulator’s announcement in April that they are in line for more than £230m in compensation could not have come soon enough.

Investors have endured an agonising four-year wait for the Financial Conduct Authority to conclude its probe into the suspension of Woodford’s £3.7bn Equity Income fund, an investigation that has centred on one of Britain’s biggest investment scandals.

With...