The network, managed by the higher education IT consortium Jisc, will have 10 times the capacity of the current system. Work on the upgrade, which will not affect existing services, is scheduled to finish by October 2013 and will satisfy demand until 2022.
According to Bob Day, chief technology officer for JANET, the replacement - labelled JANET 6 - will be invaluable for research and services such as video streaming.
"We're seeing more and more data-intensive research across many disciplines, and a lot (of it) is increasingly reliant on ... high-performance computing," he said.
"That itself doesn't require a network, but as scientists need to transfer data from one place to (another), that needs a powerful network in excess of what you would get from the normal ISP (internet service provider) industry."
JANET 6 will also cater for the large volume of data transmitted between the UK and such institutions as the European Organisation for Nuclear Research (Cern), and service unpredictable information needs in fields such as biomedical sciences, genomics and climate science.
Increased capacity will also be essential to get the best from the multi-university collaborations being pushed by the government, such as the Engineering and Physical Sciences Research Council's five high-performance computing clusters.
The government's capital investment, which is separate from Jisc's ?90 million annual core budget, cements JANET's place as a stable part of the organisation's services during a time of upheaval.
Following an independent review of Jisc in February 2011, which recommended that the body shrink its remit and budget, staff and users are awaiting the outcome of a transition process that will cut both the organisation's budget and its activities in 2013-14.
Dr Day said that as one of Jisc's key services, JANET would continue to be a focus while the body was restructured.