Source: GOV.UK
Amended late payment legislation [came] into force on 16 March 2013, implementing European Directive 2011/7/EU on Combating Late Payment in Commercial Transactions. The amended legislation will make pursuing payment a simpler process across the European Union, reducing the culture of paying late and making paying on time the norm.
Under the new rules, debtors will be forced to pay interest and reimburse the reasonable recovery costs of the creditor, if they do not pay for goods and services on time (60 days for business and 30 days for public authorities).
https://www.gov.uk/government/publications/late-payment-directive-user-guide-to-the-recast-directive
Other
Eight in 10 firms have not updated T&Cs to take advantage of new rules on late payment: http://www.supplymanagement.com/news/2014/eight-in-10-firms-have-not-updated-tcs-to-take-advantage-of-new-rules-on-late-payment