What speed can I have

To find out what ADSL services are available through BT on your telephone line use the BT number checker which will list the speeds you can have. The wording of the results box is conservative and indeed the whole system is intended to only offer speeds that are very likely to work, so it may not offer you a faster speed that might work in practice but falls outside the current "rules".

Local loop unbundlers have different systems and may offer faster services, visit samknows.com for a checker that includes LLU providers and cable broadband services.

Currently the maximum speed offered by ISPs using BT is 2Mbits/s. If a line isn't capable of 2M the checker will say "may be available" and "However, due to the length of your line, an engineer visit may be required, who will, where possible, supply the broadband service." For 2M it says "Our initial test on your line indicates that you should be able to have an ADSL broadband service that provides 2Mbps, 1Mbps, 512Kbps or 256Kbps download speed."

Note that the number checker looks the number up in a database that is periodically updated. It doesn't do a live line check. One ISP provides a phone based version of the checker at 0870 833 5155 - you can check any BT line by calling this from any phone (costs <8p/min from a BT line, others may vary).

With a few exceptions all BT exchanges offer the full range of speeds from 256k up to 2Mbits/s. The exceptions are "Exchange Activate" exchanges, primarily in Scotland, where only 512k is available from up to 5 ISPs, rather than the normal choice of over 100. The checker will only offer 512k on these, with no mention of 256k, and it will say "Your exchange has 512Kbps ADSL broadband service. Our initial test on your line suggests that you should be able to have ADSL broadband service that provides up to 512Kbps download speed, but the upstream bandwidth will vary according to the length of your telephone line."

The wording of the results page is conservative and not personalised to your line, in other words it doesn't say "may be available" because it thinks your particular line is dodgy, it says that for all lines with a maximum speed below 2M.

The worst message on the checker is that ADSL is "Very unlikely" to work. This is given out on the longest lines. In these situations it may be wise to start with the lowest speed product with a modem speed of 288 kbps, for example Zen Home250 which has the best chance of success on a long line and can be upgraded if the line proves capable of faster speeds.

Note that some ISPs supply "150" or "250" services that are actually 576 kbps modem links with a data flow limiter applied, these have no distance advantage over standard 512 kbits/s products. Zen and a couple of other ISPs use BT Wholesale's Home250 product that has an additional range of perhaps 500m compared to 512k.

Finally, pay attention to the last paragraph of the number checker result. This flags up if there are any problems with the line like an order already placed for ADSL, an incompatible product or a service active on the line. If ADSL is already present the somewhat confusing message will be :-

"Note: If you have an ISDN or Home Highway service connected to this number and you wish to purchase Broadband ADSL, this can be arranged through your Service Provider. You will only be able to keep one of your ISDN / Home Highway telephone numbers - generally you can choose any of your numbers but there are some rare exceptions. If you have an existing Broadband ADSL service and wish to change service providers then please contact both your new and existing service provider to have this service transferred."