By Martin HickmanDAY 30 - Andy Coulson's lawyers today revealed his defence to the suggestion that his instruction to "do his phone" was a command to hack the phone of reality TV contestant Calum Best.At the phone hacking trial at the Old Bailey, Timothy Langdale QC, representing Mr Coulson, explained that the editor of the News of the World was merely ordering a check of one of the paper's phones as part of a leak inquiry.As part of the prosecution case, the jury has been told of an email which Mr Coulson sent to an executive on the redtop Sunday tabloid about a forthcoming kiss and tell story on Mr Best.On being told by the executive, of whom Mr Coulson had inquired "You think Calum a leak?" - that Mr Best was "bragging I have close mates inside NotW", Mr Coulson's three-word response was: "Do his phone."Today, Mr Langdale explained the context to Mr Coulson's email, dated 20 May 2006.In an email dated 11 May 2006, Mr Langdale told the jury, Stuart Kuttner, NoW managing editor, had received billing data for a phone belonging to reporter Rav Singh, who had dealt with Mr Best in the past.Mr Langdale said: "In early April it was clear from submissions made on behalf of Mr Coulson in preliminary submissions [pre-trial hearings which could not be reported at the time] that Mr Coulson's case was that "Do his phone" was not an instruction to hack Calum Best's phone but to check on the billing of another News of the World phone for a suspected leak."Mr Coulson and Mr Kuttner deny plotting to hack phones at the trial, which is nearing the end of its seventh week. The other five defendants also deny all charges.