BT is to double the speed of its Infinity 2 fibre optic broadband service to 76 Mbps, but only for customers that extend their contracts first.
To take advantage of the offer, users will have to agree to a new 12 or 18-month contract at no extra cost.
The company is also increasing upload speeds of its Infinity 1 broadband offering from 1.9Mbps to 9.5Mbps. Download speeds would be 38Mbps on this package.
John Petter, managing director of BT's consumer division, said: "BT believes that fast upstream speeds are vital given how people now use the internet and we are distancing ourselves from the competition by providing the UK's fastest upload speed. "
The telco is still way behind the speeds offered by rival Virgin Media, who promises users a theoretical maximum of 120Mbps. Even so, BT still claimed its upload speed is the UK's fastest.
However, experts have warned that, despite the increase in speeds for some customers, others are still in the slow lane.
Citing data from almost 1.7 million speed tests carried out between August 2011 and January 2012, Ernest Doku, technology expert at uSwitch.com, said almost a quarter (23 per cent) of home broadband users are saddled with broadband speeds of less than four Mbps.
"We shouldn't forget that if - as the Government envisages Britain is to have the best broadband network in Europe by 2015, it is also crucial that this investment is distributed fairly across the country," said Doku.
