A jury is set to retire to decide whether or not a former airman downloaded child pornography on to his home computer in his barracks room.

James Richard Poole, 33, had more than 6,000 pornographic images on his computer at Blackburn Barracks, RAF Leeming, in North Yorkshire, when it was seized by Ministry of Defence police officers.

Among a vast array of illicit pictures found on the hard drive of his desk top PC and two compact discs, the officers found sordid Internet pictures of underage girls.

Poole, of Dulford Court, Hollingswood, Telford, Shropshire has always denied any knowledge of the pictures, and claimed he did not know how they had got on his computer.

Teesside Crown Court today heard a computer expert say that there were enough picture files on his computer and CDs to fill the equivalent of more than 100 30-volume sets of Encyclopaedia Britannica.

He said that files had been created on Poole's PC after he was arrested, but he could not say how they had got there.

The jury was left to decide whether or not foul play by Poole's arresting officers had led to images appearing on the computer.

Jonathan Vogler, a computer consultant from Leeds, said he believed MoD police officers had gone about their investigations in an unprofessional manner and had not followed police guidelines on the best way to deal with computer-related allegations of crime.

Detectives who searched Poole's barrack room on August 9 last year did not immediately switch off his computer, despite the fact it was connected to the Internet and network to a computer in his next-door neighbour's room.

Prosecutor Peter Johnson asked Mr Vogler: ''Is it not the case that what you are suggesting is that one or other of these officers has deliberately accessed the Internet and obtained these files from the Internet?''

Mr Vogler replied: ''I don't think it is my job to suggest things, only to tell the court what I found.''

The computer expert told the court there were a number of ways in which information could have found its way onto Poole's computer other than him downloading the files himself.

He said: ''There are three possibilities. One is that because the connection to the Internet had been left on things were happening from the Internet onto the computer.

''I am not very happy with that because normally if a computer Internet connection is just left on it dies after a period of idleness.

''But it is possible that the Internet site that was being accessed could have had some arrangement to prevent that. I am very much uncertain about that.

''The possibility number two is that there was an Internet connection from the computer next door via this computer; and possibility three is that someone at the defendant's computer was continuing to access the Internet.''

Mr Johnson told the court that it ''beggars belief'' that MoD police had spent two hours after Poole's arrest downloading sordid child pornography images on to his computer.

He said: ''On the computer owned by and, we submit, controlled by and programmed by the very intelligent Mr James Richard Poole, that he knowingly was searching the 'Net' for and downloading images of underage girls.''

Poole denies 12 charges of making indecent photographs of children.