BT is letting web users on ADSL2+ connections increase their upload speed by sacrificing some of their download speed.

The company's new product, Annex M, will be available to customers of BT and other ISPs that use BT'S 21CN network.

Web users will see their upload speeds boosted by between 200Kbps and 1Mbps, while their download speed will reduce by between 10 and 15 percent. BT also says the service offers a guaranteed upstream throughput of 85 percent of maximum speed available on that line between 8am and 5pm Monday to Friday. However, this excludes public and bank holidays.

Annex M is aimed at consumers who upload lots of photos, online gamers and businesses with remote staff that send and receive large files regularly.

Trials by communications provider Entanet showed that those located close to exchanges were receiving upload speeds that exceeded 2.5Mbps. But speeds dropped to 1Mbps for those further away from the exchanges.

BT said those further away from the would see minimal gains in upload speeds compared to the loss of download speed.

"Entanet has been significantly involved in the trials of Annex M and has been very impressed by the results experienced. So far we have seen that, in the majority of cases, the actual performance of Annex M has been well beyond BT's (and Entanet's) original expectations," Entanet said in a blog.

Annex M will be available later this month. It is unknown how much the service will cost the end-user. BT is charging ISPs £7 per customer for Annex M.

See also: BT to increase line rental from October