The series is expected to begin in July, with Front Row presenter Mark Lawson announcing: "Torchwood: Miracle Day begins on BBC1 next month, alongside Radio 4's Torchwood drama." after speaking to writer/producer Russell T Davies on the show. Davies himself believed it would be during week 28, telling On The Box: "it's something like Thursday July 14th here, that's the plan, so you only have to wait six days." However, BBC News muddied the waters somewhat, reporting after the preview of episode one that: "The series will air in the US in early July and be shown later in the summer on BBC One."
Based on the press release it would currently seem that Torchwood won't begin on UK television until at least a week after its premiere in the United States. However, as always, the Press Office states:
Scheduling information in Network TV Programme Information is subject to change.
Update: the BBC Press Office issued a tweet on Friday 24th June to say: "Torchwood schedule is still being determined and once there's a date, we'll let you know."