Over the last week, Kevin Federline’s legal team have subpoenaed Britney Spears‘ cousin (and former assistant) Alli Sims, another former assistant Shannon Funk and Britney’s bodyguard Daimon Shippen but now they believe they’ve served a critical figure in the case against Britney - the representative of from Promises Treatment Center in Malibu where Britney spent time earlier this year.

Kevin’s lawyer Mark Vincent Kaplan confirmed to Us Weekly that “an executive administrator from Promises rehab facility was served with a subpoena” yesterday morning and the unidentified figure will be required to give evidence about Britney’s stay at the facility and the treatment she received.

The reason for Britney’s stay at the centre has never been confirmed but it is generally thought she was in rehab for alcohol and possible prescription drugs issues after months of partying. However, Britney is thought to believe she was pushed unnecessarily into the programme by her family, particularly mum Lynne Spears, and then manager Larry Rudolph, and that she was actually just suffering from a bout of postpartum depression.

Kaplan told the magazine that the deposition given by the Promises administrator will answer some questions about Britney’s mental health and any present addictions: “Kevin is pursuing relevant information from all relevant sources… There is a significant strategy in place that Kevin is going to pursue whatever he needs to do to protect his kids.”

Meanwhile at the end of a hard week, Kevin himself was snapped partying in Las Vegas in the early hours of Saturday morning. An onlooker told the magazine: “He was slugging down Patron, Jagermeister and Grey Goose right from the bottle, gulping it down as if it were water. It seemed like he just wanted to get wasted.”