An editorial in the Guardian says Sri Lanka's mankading of Jos Buttler was well within the rule books, and so it should be England who apologise for the incident, not the visitors.
In the words of Sir Donald Bradman: "If not, why is the provision there which enables the bowler to run him out? By backing up too far or too early, the non-striker is very obviously gaining an unfair advantage." If it's good enough for the Don, it should be good enough for Alastair Cook. It's England who should apologise.