The best services on that exchange would be from Sky or BE (neither of whom seem to apply any cap on the amount of downloaded data).
Having said that if he really only downloads 10GB a month he could also go with O2 (the same network as BE, but one where they apply quite tight download limits on their cheaper products).
With a 28dB attenuation he'll likely connect well above 10-12Mbps.
I'd say BE Value would be suitable @ £14.08 a month, download speed up to 12Mbps upload speed up to 1.3Mbps (and he'll probably be able to get these maximums). This product has unlimited download allowance.
Only problem is BE don't do e-mail, so he'd have to get this elsewhere (typically around £1 a month plus maybe £3 a year for his own .co.uk domain name (to go with the e-mail).
O2 'basics' @ £13.28 a month is essentially the same product, but with a 20Mbps maximum download speed but a 20GB a month cap on data usage.
With Sky, BE and O2 he will also be able to have his voice line rental and calls package moved across to his new ISP (all are cheaper than BT - unless you pay BT upfront for 12 or 18 months of calls).
ADSL2+ with BE
DL Sync around 4.8Mbps
UL Sync 1088kbps
DG834GT with DGTeam firmware