Milestone Resources Group, which is owned by Landmark’s chief executive officer Micky Jagtiani, disclosed its holding after buying more shares in the UK retailer on 15 December.
All investors have to disclose their holdings when they exceed the 7 per cent threshold under London Stock Exchange rules.
Debenhams’ shares hit a record low of 75.5p on 17 December. The company floated on the stock market at 200p in May 2006.
Gulf investors have bought stakes in a series of major Western retailers during 2007.
In August, Istithmar, a UAE-based investment fund, won control of Barneys, a US department store chain, with a bid of $942m.
In the same month Delta Two, an investment fund backed by the Qatar Investment Authority, built up its holding in J Sainsbury, the UK’s third-largest supermarket group, to 25 per cent. It later pulled out of a full takeover bid for the retailer.