The Infinity Option 1 £19.99 per month BT deal comes with a 20GB monthly usage allowance, subject to a fair usage policy. Option 2 costs £24.99 and is listed as unlimited, subject to the same fair usage policy.

The cheaper BT £19.99 per month option also comes with a £50 connection charge. Both options come with a 18-month contract.

Upstream speeds, at up to 10Mb/s (2Mb/s on the £19.99 per month package), will be the fastest in the UK, more than 6 times faster than Virgin Media's fastest service, giving customers far greater interactivity BT insists.

The cable giant hit back, accusing BT of misleading consumers because Virgin Media's service is actually faster. BT's service runs at 40Mb per second while Virgin Media's is 50Mb per second.

"We're not sure why people in the UK would want to wait for BT's 40Mb service which hasn't launched yet, when they can already get Virgin Media's great value 50Mb service," said a Virgin Media spokeswoman.