Europe’s biggest commercial property company is to buy Westfield, the Australian company behind the UK’s two highest-earning shopping centres, in a $25 billion deal that will create the world’s largest mall operator. French Unibail-Rodamco  plans to roll out Westfield centres in Europe and the US. The planned tie-up comes as the growing number of people buying items online, fuelled by Amazon, forces shopping centre operators to focus on their best assets.