A major development on one of Kent’s busiest high streets has been put up for sale for £6m casting uncertainty over the project. Setha Canterbury was leading plans to transform the city’s former Nason’s department store into a Brighton Lanes-style retail arcade, with a food and drink hall, public open space and 66 flats. But the £30 million scheme has long been held up by concerns over wastewater pollution leaching into the Stodmarsh Nature Reserve in Canterbury. Now, the firm is under the control of a receiver after defaulting on a loan taken out to buy and develop the scheme. With the lender…