As BS indicates, pauses with the BBC iPlayer are almost certainly due to poor download speeds. Many 'bargain basement' broadband deals limit certain types of download speeds at peak times. Additionally, the download speeds achieved by each user are affected by the activities of others getting their internet service via the same telephone exchange. If you're trying to use the iPlayer at the same time that everyone else in your street is using it (or, for example, downloading movies on peer-to-peer networks), the chances of you experiencing problems are greatly increased.
The UK's ISPs hate the BBC for developing the iPlayer. It puts their systems under strains that can't really be coped with (without massive investment in recabling the country with fibre optic networks). You might get better results with the iPlayer by:
(a) paying more for a better broadband service ; and/or
(b) using it only at off-peak times.
The British government has committed itself to ensuring that everyone in the country will be able to access broadband, at a minimum of 0.5Mb per second, within 10 years. Such speeds simply aren't good enough for applications such as the iPlayer. South Korea's target for the same period is that everyone in their country should have access to broadband speeds of at least 100Mb per second, with many getting 1000Mb per second. When we finally catch up with that (in, perhaps, 30 years time) the iPlayer (or whatever replaces it) will finally become reliable.
Chris