The US law firm won the mandate after being recommended to the Cheltenham-based company by the Royal Bank of Scotland (RBS), which coordinated the deal.
According to John Bennett, finance director at Westbury, RBS suggested two firms for the company to use on the placement, £100m of which has been borrowed over a 10-year period, with the remaining £50m secured over seven years.
Bennett said: "We instructed White & Case on the bank's suggestion, since they hold the firm in high regard."
However, he added that the company would still continue to use its usual adviser, Freshfields, on other matters.
White & Case partners Ian Clark and Andrew Weiler headed up the deal.
Although White & Case has a longstanding relationship with RBS, Weiler says that over the last six months the bank has instructed the firm on a large amount of private placements, which have become US pension funds' investment of choice, given the dour market conditions blighting equities and publicly traded debt.
"We've worked for the bank for many years," said Weiler, "but over the last six months private placements have become more active."
Recent deals have included the $850m (£538m) private placement for Scottish & Newcastle, while the firm has also landed instructions for fundraisings by Johnston Press and Vivendi Environmental.