You can now catch up with the residents of Albert Square or enjoy an old episode of Father Ted over the internet, with download services from the BBC and Channel 4. But before you log on, check the small print in your broadband contract. Downloading large programme files could add extra charges to your monthly bill and slow down your connection. The BBC iPlayer, launched last year, lets you download programmes broadcast on BBC channels in the past seven days to watch on your computer. Channel 4 runs a similar service, called 4oD, and other internet television services are available.

Some broadband contracts limit the amount of data you can download to as little as 1,000Mb, or 1Gb, a month. If you are an occasional internet user, a low allowance will not be a problem. Surfing the internet for 60 minutes uses up only 0.02Gb of your monthly allowance. Downloading an album takes just 0.06Gb.

But when you consider that an hour-long TV programme, such as Holby City, downloaded from the BBC’s new service, is roughly 600Mb in size, two episodes could easily send subscribers over their limit. A half-hour episode of EastEnders is 0.27Gb and hour-long shows are 0.6Gb. Meanwhile, five hours of radio over the internet is about 0.6Gb and a film on some download sites could be up to 4.6Gb.

“There is a lack of awareness when it comes to download caps. Providers focus on the connection speed, but don’t cover the amount you can download each month,” says Rob Barnes, of Moneysupermarket.com, the comparison website.

Major players in the market such as BT, Orange, AOL and Tiscali, along with smaller providers, such as Namesco and Madasafish, offer entry-level broadband tariffs with a monthly charge of £12 to £15 and download limits of between 1Gb and 10Gb.

Long-standing broadband customers could also be on contracts with prohibitive allowances.

Mr Barnes says: “Generally, smaller companies such as Namesco and Madasafish have the smallest download caps. They don’t have the economies of scale of the larger providers, and so recoup money from the customer by capping downloads.”

Providers levy an array of charges for going over your limit. Broadband customers on Eclipse pay £1.75 per extra gigabyte, while Pipex charge a minimum of £3 for every 3Gb that you are over. BT adds 30p per gigabyte over your limit from the second month, but you are more likely to be pressurised to upgrade your tariff.

For those on “unlimited” downloads, some providers reduce the speed of your connection if you download too many large files. On Virgin Media, for example, your speed could be cut by three quarters if you download too many programmes in peak hours, between 4pm and 9pm.

Michael Phillips, of Broadbandchoices.co.uk, a broadband information website, says: “Even if you have unlimited downloads, you will also have a ‘fair usage policy’, which imposes penalties for ‘excessive usage’. Services such as the iPlayer could quietly lead users over download caps or in breach of fair usage policies.”

If you have downloaded the iPlayer software, rather than just streaming episodes directly from the BBC website, an added danger to your usage is that it operates on a peer-to-peer system. Programmes that you have saved on your computer can be uploaded and sent to other users across the internet. “Running in the background at all times, this kind of service will degrade your internet connection speeds and plough through your usage limit,” says Mr Phillips. You can change the settings on the iPlayer so that you are not always part of the peer-to-peer network.

Some providers offer free download monitors, which keep a tab on how much of your allowance you have used up. If your provider does not, you can get a free monitor from Broadbandchoices.co.uk.

However, if you find that you are exceeding your download usage, the easiest option could be to upgrade to a new tariff, or switch providers.

Mr Barnes says: “It is a massively competitive market. If you’re on an older contract with a limit on downloads you should switch. Broadband is almost free now with some providers. You couldn’t fail to save money.”

CASE STUDY: A learning experience

Brian Gordon enjoys BBC science and natural history programmes, such as Horizon and Natural World, and regularly downloads episodes using the iPlayer software.

Since discovering iPlayer, Mr Gordon has upgraded his PlusNet broadband contract so that he can download 3Gb of data a month. The 60-year-old, from Lydney, Gloucestershire, describes himself as internet-savvy, but admits that using the iPlayer was “not as straightforward” as he had first thought.

He is careful not to exceed his download limit, but is easily able to top up his allowance with his PlusNet account, which includes a download monitor.

Having learnt more about the iPlayer, he shuts down the software when not using it. He says: “I close it down because the peer-to-peer aspect of iPlayer means that someone could be uploading programmes using my bandwidth.”

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