US activist investor Ancora Holdings Group is calling on UK self-storage operator Big Yellow Group to explore a potential sale after acquiring a stake of more than 4% in the company, according to a report by Bloomberg.

Ancora believes Big Yellow is materially undervalued and has urged its board to undertake a comprehensive strategic review, including a potential sale process involving financial sponsors and strategic buyers.

James Chadwick, President of Ancora Alternatives, disclosed the investment and campaign at the Sohn San Francisco Investment Conference on Tuesday, arguing that Big Yellow's valuation represents an attractive opportunity for prospective acquirers.

The activist investor estimates that Big Yellow's shares are trading at a 40% discount to net asset value, reflecting weak UK economic growth, a subdued housing market and the company's capital-intensive development pipeline.

Ancora argues that the company's London-focused property portfolio, pricing power and growing customer demand make it an attractive acquisition target. The fund identified KKR, Heitman and Nuveen among potential financial buyers, alongside US self-storage operators Public Storage and Extra Space Storage.

Shares in Big Yellow rose as much as 6.3% in London on Wednesday, their largest intraday gain in more than six months, although the stock remains down approximately 20% year-to-date.

The campaign follows previous takeover interest in Big Yellow. In October 2025, the company confirmed discussions with several parties over strategic options, including a potential sale, after Blackstone disclosed that it was considering a take-private transaction. Blackstone subsequently abandoned those plans in December.

Ancora believes the company should have pursued a broader sale process at the time and maintains that potential buyer interest remains strong.

Big Yellow, the UK's largest self-storage operator, reported annual revenue of £209.1m for its 2026 financial year, up 2% from the previous year.

The campaign represents one of Ancora's first major activist investments in the UK. The Cleveland-based investment firm manages approximately $12bn in assets and has conducted more than 30 activist campaigns over the past six years, including at US railway operator Norfolk Southern.