Postcodes for high speed (8Mbps+) ADSL

I currently live in Leeds but will shortly be relocating to Northwest London (possibly Mill Hill area): does anyone know what postcodes in that part of the country are close enough to their exchanges to get 8Mbps+ ADSL? If not, is there a way to find this out? For example, would it be possible to write a script to poll BT's availability checker and get estimates for every postcode in an area?

If not, does anyone know if cable (i.e. Virgin Media) broadband is affected in this way? That is, does cable broadband speed vary depending on your postcode, or is it relatively static due to the nature of the technology?

Try Samknows mapping http://www.samknows.com/broadband/mapping/mapping.php

Cable broadband throughput speeds can vary between difference areas due to the loading (contention) in their network

Thanks! Exactly what I needed.

You cannot guarantee the postcode accuracy.

Some friends tried that and it suggested 2Mb service would be available - they have finally got 256k (fixed) and BT are about to try and squeeze an extra little out to get a 512k connection.

Their immediate neighbours in a block of 4 cottages are all much the same, but 400m along teh road, the two houses get 2Mb and 8Mb services. The cables are routed totally diferently so you may or may not succeed.

Yes, I'm aware that different houses in the same postcode might be on different circuits and so might have different maximum speeds. I'm planning to ask for phone numbers for all the properties I look at so I can check properly.