Moyles's decision to leave is said to be down to the timing of the show, which airs at 7pm -- just an hour after Moyles finishes his afternoon show on BBC Radio 1.
O'Connell is to take over the show, which is made by Chris Evans' production company UMTV, for an eight-week stint starting next month.
The programme will be called 'Live with Christian O'Connell' and will stick to the same format of games, showbusiness news and audience participation.
O'Connell's breakfast show was named number one in Campaign's book of lists for 2002. It is believed to be a firm favourite among media buyers and is the 12th biggest breakfast show in London.
The show has grown in popularity, adding 100,000 listeners in the third quarter of 2002 and he won the best radio presenter award at the 2002 NTL Commercial Radio Awards.
No doubt Five will be hoping O'Connell's appeal will be more transferable to television than that of Moyles. The network is understood to be aiming for an audience of 500,000 viewers, but the programme was typically watched by between 300,000 and 400,000 -- about average for that slot on Five.
Some nights, however, the show only drew an audience of 100,000.
The show's poor performance so far will come as a disappoinment to Five, as it was one of the programmes the channel relaunched with.
Moyles is understood to be in talks with UMTV about fronting a weekly entertainment show for the channel.
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