Shares of FTSE 250 self storage operator Big Yellow Group rose more than 5% on Wednesday after activist investor Ancora Holdings Group urged the company to explore a sale, arguing that its shares significantly undervalue the business.

Ancora, which holds a stake of more than 4%, called on Big Yellow's board to launch a comprehensive strategic review and solicit offers from potential strategic and private equity buyers.

It argued that a sale represented the best risk-adjusted route to delivering full value for shareholders following an extended share price decline and the failed take-private approach by Blackstone in 2025.

Ancora estimates Big Yellow’s intrinsic value at £12.36 per share, implying at least 54% upside, and said the shares trade at a discount of almost 40% to net asset value (NAV). It also pointed to the company’s valuation of 14.6 times forward core earnings, compared with its historical average of 21.1 times.

The investor said Big Yellow’s portfolio of predominantly freehold properties, concentrated in prime London locations, provided a competitive advantage through strong pricing power and resilient demand. It estimates that London-based stores generate 70% to 75% of the group’s total core earnings.

Headquartered in Bagshot, Surrey, the Yellow Group operates a network of 115 self-storage stores nationwide across the UK, with more than 6.7 million square feet of storage space serving over 71,000 customers. Its portfolio includes 24 Armadillo Self Storage stores, a separate brand owned by the group.

Alongside a potential sale, Ancora urged the company to consider divesting non-core assets, rebranding or selling its Armadillo business, realising value from its property development pipeline and buying back undervalued shares.

Ancora said it intended to engage constructively with the board to unlock value, adding that interest from potential buyers remained strong despite the failed Blackstone approach.

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